Membrane

-------------------International news and reports on membranes

Breathable roofing membrane tile underplays in cold roofs

Roofing Membrane for Flat Roofs

House Membrane Wiki

Roofing Membrane Types

Roofing Membrane Manufacturers

Roofing membrane

Roofing foil patent

Breathable roofing membrane underplays in cold roofs

Breathable membranes have been used in buildings for many years now and, more recently, in cold pitched roof constructions without traditional eaves ventilation. The benefit of reduced heat loss and not having to incorporate ventilators has seen their use grow but at the same time has attracted noticeable comment both from supporters of the application and from detractors who favour traditional ventilation solutions.

In light of this, the BBA has prepared this short article to clarify our view as independent assessors of ‘fitness for purpose’ of products and their application.

We have adopted a ‘Question and Answer’ approach to allow the easy identification of items of particular interest and/or concern to readers. The views expressed here are based only on the BBA’s experience in assessing breathable membranes in a number of applications over recent years. Products or applications which are outside the scope of published Agrement Certificates or national Codes of Practice have not been assessed by the BBA and are not addressed in this article.

What is a breather membrane and how does it work ?1
The particular membranes in question typically comprise spunbonded polypropylene or spunbonded polypropylene/polyethylene laminated either side of a micro-porous polypropylene or polyethylene film.
Monolithic spunbonded membranes are also used. They have a structure that is sufficiently fine to prevent liquid water penetration in service conditions, but not too fine to prevent the transfer of water vapour (molecules of water in air), see figure 1.
All materials, including vapour control layers, have a finite permeability to water vapour transfer. However, in the context of this Article, a breathable membrane is a material which, in service conditions, is sufficiently permeable to water vapour transfer to adequately limit the risk of condensation in roofs.

Current published definitions include the following:
BS 5250: 2002 section 3.2 “Breather membrane” – vapour permeable membrane with a vapour resistance less than 0.6 MNs/g. The Standard goes on to describe the use of ‘Breather membranes’ in walls.
BS 5250: 2002 section 3.26 “Vapour permeable underlay” – Pitched roof underlay which meets the recommendations of BS 5534-1 and NFRC TB6 and is additionally water vapour permeable with a vapour resistance of less than 0.25 MNs/g
These two figures can also be expressed as water vapour transmission rates of at least 341 or 820 g/m2/day respectively, when tested under standard conditions of 25o C and humidity of 0% rh and 75% rh on each side of the membrane.
The function of these membranes is to provide all of the normal demands made on a roof underlay and at the same time allow water vapour egress without making specific provision for ventilation.

How widely are rhe membranes used and in what applications ?2
A2 Breather membranes have been used abroad in construction since the 1970’s. Membranes were first Certified by the BBA in 1982 as sheathing membranes for timber frame walls and as roof tile underlays in conventionally ventilated cold roofs. They were subsequently approved as roof tile underlays in warm roof constructions in 1982 and most recently in cold non ventilated roof constructions in 1999. At the time of writing this article, Certificates for roof tile underlays used as part of a cold unventilated pitched roof system in dwellings have been issued as shown in Table 1

Can the membrane be used simply ‘instead’ of conventional eaves ventilation ?
Only if a number of measures are taken to limit the ingress of water vapour into the unventilated space. In this regard, the roof system must be considered as a whole from ceiling to roof tiles, including the following design points: - all penetrations into the roof space must be properly sealed - loft hatches must incorporate effective compressible draught seals - the rooms below the ceiling must include provision for the dispersal and rapid dilution of water vapour in accordance with the Building Regulations, including extractor fans in rooms that may experience high humidity - All water tanks in the loft space must be covered - Any vent pipes should be arranged so that they do not discharge water vapour into the loft space

What are the advantages of using the membrane unventilated system ?4
One of the main advantages is reducing the amount of heat lost by air leakage through the ceiling and from the loft space to the outside. Up to 25% of the heat lost through a conventional roof system is by this mechanism. The unventilated roof ‘system’ will reduce this mechanism of heat loss, more so if the underlay laps are sealed. In addition, not having to provide eaves and ridge ventilation can help to save time and cost on site and can give a more desirable appearance to the finished roof.

What are the disadvantages of using the membrane system ?
Extra time and care is needed to ensure that penetrations into the ceiling are properly sealed and that the loft space is protected from sources of water vapour, in accordance with the requirements of the Certificate.
If the ceiling is constructed without due attention to sealing joints and around penetrations, the opportunity for moisture ingress into the loft space and consequent risk of condensation occurring is increased. This is also true of conventionally ventilated constructions where the effect of wind movement over the roof can reduce the air pressure in the loft space and ‘suck’ moisture laden warm air from the living space into the loft space. However it is recognized that the rate of moisture removal via the ventilated and unventilated approach is not the same. It is therefore important that the ceiling is sealed to an appropriate level. BBA computer modeling of the behavior of roofs has assumed effective ceiling ‘defect’ areas of up to 10 square mm per square metre of ceiling. See also Q/A 6, 7 and 11.There are reports concerning ‘flapping-noise’ in roofs incorporating some types of permeable roof tile underlay membranes in certain wind conditions. The BBA has, however, only received a very limited number of reports in this regard and therefore do not view it as a fundamental problem.

How did the BBA assess the products in unventilated roof membrane applications ?
The suitability of the membranes as conventional roof tile underlays had already been established by means of conventional assessment and test programmes. The absence of conventional ventilation at eaves added the ‘new’ dimension which the BBA addressed by developing, in partnership with membrane manufacturers and suppliers, a sophisticated software package. This program used classical physics to model the dynamic movement of vapour in various roof constructions with a range of properties/parameters such as ; - internal and external humidities and temperatures - vapour permeability of the roof tile underlay - vapour resistances and defect areas for all layers in the ceiling and roof fabric - wind velocity over the roof The modelling indicates that the magnitude of the following parameters are of particular importance:
- permeability of the roof tile underlay
- rate of vapour passing through the ceiling

Are the installation measures in Q&A3 practical to achieve ?
Yes. The BBA has conducted a number of visits to sites in progress and completed buildings. See also Q&A6 Q8 BS 5250 : 2002 says that you have to ventilate ? A8 Section 8.4.4.2 of the BS does state that pitched cold roofs with unsupported vapour permeable roof tile underlays do not require ventilation to the loft space, but a ventilated counterbatten space should be provided above the membrane, by means of eaves and ridge ventilation. Regulations, such as Requirement F2 Condensation in roofs to the Building regulations 2000 (as amended) (England and Wales) are mandatory and call for ‘adequate provision to be made for preventing excessive condensation in roof spaces’. Meeting this Requirement can be demonstrated by following the guidance in the BS but it doesn’t have to be followed if other means can be used to show compliance. The BBA assessment is for a roof ‘system’ and provided that the installation is in accordance with the requirements of the relevant Certificate, the mandatory requirements, ie the Regulation, will be met. See also Q&A3. At the time of writing, BS 5250 is being revised for unventilated roofs.

How durable are the membrane system ?
In normal conditions found in roofs, the membranes are durable and can be expected to have a life comparable to that of traditional roof tile underlays. Specifiers should however follow the requirements of the relevant Certificate relating to the period for which the underlay can be exposed to the elements before slating/tiling and on the use of eaves guards for open eaves constructions.
With regard to water vapour permeability, the BBA assessment included measurements of the effect of heat ageing, effect of UV light exposure and of accelerated dust/debris accumulation and found no discernible reduction in performance.

Do I need a vapour check ceiling ?
No but it can help. It is important to remember that vapour will pass through the path of least resistance in a ceiling. Gaps and cracks will provide an effective ‘short-circuit’ however high the vapour resistance of the rest of the ceiling is.

What do I do about sources of moisture in the loft space
Water tanks should have lids on and vent pipes arranged to avoid venting moisture into the loft space.

Do I need counter battens ?
In general, counter battens are not required if the underlay is draped between rafters, ie a nominal 10 mm. If however it is not draped but pulled taut, counter battens are applied. Readers should refer to specific Certificates for the holder’s detailed installation instructions.

Can you have unventilated loft spaces when timber sarking is used ?
Yes, with the traditional Scottish practice of planks nominally 100 mm wide with a 2 mm gap either side. Their use with large OSB, chipboard or plywood timber panels, 2440 mm by 1220 mm, has not been approved by the BBA.

Does the membrane have to run parallel to eaves or perpendicular (eaves to eaves via ridge)?
Traditionally, roof tile underlays are laid in runs parallel to the eaves with subsequent runs ‘weather lapped’ by 150 mm. Some Certificate holders have had an alternative approach also assessed, where the underlay is drawn from the eaves, over the ridge and back down to the eaves on the opposite side of the building. This entails the use of a device to hold the roll of underlay horizontally and allow it to be unwound. Counterbattens are also needed to secure laps between adjacent runs of the underlay. Users should refer to the relevant Agrement Certificate for full details of this alternative method of installation.

What type of membrane roof covering can be used ?
The issued Certificates cover conventional slates and tiles installed to the relevant clauses of BS 5534-1: 1997. The modelling assessments referred to in A6 included tightly fitting synthetic tiles with ‘open’ areas down to 475 mm2 per square metre and predicted some slightly longer durations for condensation events, but at levels and durations that were still acceptable. When considering tightly fitting tiles and slates, specifiers are advised to check with the tile or slate manufacturer in case they have particular design requirements, for example a ventilated space beneath them.

What happens to ‘constructional moisture’ ?
The amount of constructional moisture present in a new building depends on the materials used and type of construction. The risk of condensation is however greatest when there is significant drying out taking place and cold temperatures. This may in some circumstances lead to condensation during the first heating season, but should not persist into a second heating season in a properly designed and constructed roof.

What happens if the membrane system is not installed properly or there is a condensation problem ?11
Whether a product or system is innovative or not, things can go wrong. In the first instance you should contact the installer or the Certificate holder. If the issue is not resolved satisfactorily, contact the BBA.

Has the BBA received any complaints about these types of systems ?
Yes, four have been reported. One complainant did not reply to requests for fuller details of the failure, the other three are currently under investigation. It is always important to bear in mind that very little building technology is immune to poor workmanship or inappropriate design. The question is often one of robustness and education. It is also important to note that even established solutions can sometimes fail

Is it better to ventilate or not ventilate ?
Both approaches work although particular building types and constructions may favour one approach over the other.

Conclusions
The principle of designing and building a roof system that does not include traditional eaves ventilation is sound and practicable, provided that the design and installation instructions described in the relevant BBA Certificate are observed. The BBA has not seen any evidence that suggests that such systems will not adequately limit the risk of damaging condensation.
Note, the BBA is an independent Approval and Certification body for construction products and

Roofing Membrane for Flat Roofs

By Tim Carter
©1993-2008 Tim Carter

Summary: Roofing membranes and synthetic rubber roofing compounds for flat roofs outperform gravel roofing materials and make roof leak detection far easier. These roofing materials are basically seamless and fight UV damage. Used mostly commercially, flat roof membranes have many residential uses.

Do you have an old fashioned ballasted flat roof? This is a roof covered with gravel. The gravel is used to hold down the roofing materials in high winds and it also protects the old asphalt from ultraviolet (UV) light from the sun. UV rays really hurt asphalt. If you have one of these roof systems and a leak(s), forget about locating them. It will be virtually impossible! The gravel does a fantastic job of hiding leak locations.

Synthetic Membranes

The use of synthetic membranes has just about eliminated the need for gravel on roofs. Why? Because many of these new roof membranes are glued down to the roof sheathing. Not only that, the new membranes contain materials that resist UV degradation. If you can install a new flat roof without gravel, DO IT! It will make future leak finding much easier.
The synthetic membranes have many other benefits. Imagine being able to cover your house with just one giant piece of roofing material? No seams to worry about! It is possible if you find the right roofer and get the right membrane. Some of the membranes come in widths up to 50 feet!

The Actual Material for the membrane

Have you ever seen how a flat tire is fixed on a tubeless tire? The rubber patch is actually vulcanized to the tire's inner surface or wall with special solvents. The patch and the tire basically become one in the same. This is how some of the new membranes work. As a roofer seams pieces together or makes cuts for flashings, they can actually weld pieces of material together.
Some of the top performing materials, in my opinion, are the synthetic rubber roofing compounds. These are commonly referred to as EPDM and CSPE materials. I have installed these materials on many of my jobs where low slope roofs have caused leak problems using conventional materials. These membranes work very well where old rolled asphalt materials, hot mopped asphalt, or even shingles were used before. The only disadvantage, I can see with them is that they are not DIY friendly. In other words, you will probably need to locate a professional to install them. You must remember that this technology is not really used much in residential work. Commercial roofers use these materials most frequently. There are many residential roofers in Cincinnati that have experience with these materials. I am confident that you will find residential roofers in your town as well who can successfully install the membranes.

Where Can You Use the membranes?

The membranes have many uses in residential work. You can use them on shed roofs that commonly have low slopes or on a Cape Cod style house with a dormer. There are many older houses that have low sloped worn out tin roofs. The membranes are far cheaper to install than replacing with tin or copper!
How about chimney crickets? These are little hip roofs that are found behind chimneys. Membranes work well here. Does your house have the old fashioned tin box gutters? If so, you can reline the gutters with these membranes instead of expensive tin. An additional benefit is that you don't have to maintain the membrane like tin. Tin requires periodic cleaning and repainting.

Periodic Inspections of the membrane roof

If you have a flat roof on your house and do install a new membrane roof, I suggest that you perform an annual inspection. Since the roof is flat or nearly so, it will be easy to walk around. I urge you to inspect the roof for the first time immediately after it is installed. Take photos of the roof and close up photos of all flashing locations and seams. Keep these photos in a safe place and make sure they are clear. As you perform your annual inspection, you can refer to the photos to see if an area, seam, or flashing has begun to change. Photos are wonderful tools. As they say, "The lens doesn't lie."

Don't Do Old Asphalt Again

Don't be tempted by the lower price (possibly!) to do a quick mop over of your existing asphalt roof. Asphalt is simply old technology and is prone to failure. The system is dependent upon expert workmanship for long term high performance. Excellent workmanship is harder and harder to find these days.......

Also, you will be surprised at the warranties you can get with the membrane materials. When you sit down and analyze the cost versus the benefits, you will do well by upgrading to the membranes. So far, every membrane roof I have installed has been leak free. Some have been on for more than 12 years. If I had a low slope on my own house I can tell you that I would put an EPDM or CSPE membrane on it so fast your head would spin. Leaks cause anxiety. Don't get cheap when it comes to your roof. Buy the best and relax......

House Membrane Wiki

House membrane is in large sheets, generally fused in some way at the joints to form a continuous surface.

Thermosetting plastic (e.g. EPDM rubber). Synthetic rubber sheets adhered together with contact adhesive or tape. Primary application is big box store with large open areas and little vertical protrusions.
Thermoplastic (e.g. PVC, TPO, CSPE). Plastic sheets welded together with hot air creating one continuous sheet membrane. Can be rewelded with the exception of CSPE. Lends itself well to both big box and small roof application because of its hot air weldability.
Modified bitumen - heat welded, asphalt adhered or installed with adhesive. Asphalt is mixed with polymers such as APP or SBS, then applied to fiberglass and/or polyester mat, seams sealed by locally melting the asphalt with heat, hot mopping of asphalt, or adhesive. Lends itself well to all applications.
Built-Up Roof - Multiple plies of asphalt saturated organic felt or coated fiberglass felts. Plies of felt are adhered with hot asphalt, coal tar pitch or adhesive.
Sprayed-in-Place Polyurethane Foam (SPUF) - Foam sprayed in-place on the roof, then coated with a wide variety of coatings, or in some instances, covered with gravel.

Roofing Membrane Types

By Tim Carter
©1993-2008 Tim Carter

Summary: There are three basic types of membrane roofing for flat roof repair. These roofing materials enable you to basically shrink wrap your roof! Flat roof membranes take the roof leak worry of yesteryear out of owning a flat roof.

Types of Roofing Membrane Materials

Flat roofs have been around for ages. Old technology dates back thousands of years with respect to deflecting water. Old fashioned tar and pitch (asphalt compounds) were employed almost exclusively until 25 to 30 years ago. In fact, asphalt is still used today although its use is waning.
The new membrane products began to appear about 40 years ago. The explosion in the synthetic rubber industry and the plastics industry helped fuel this growth. The result are flat roofing products that enable you to basically "shrink-wrap" your roof! Prior to the advent of these products, you knew that if you bought a building with a flat roof, dealing with leaks would be inevitable. The new membranes allow you to be unconcerned with each rain cloud that floats over the horizon!

Three Basic Types

There are three major types of flexible roofing membranes. All of them are fairly complex and some have names that you can barely pronounce. I happen to like the products in the first group - those being the Thermoset types.

Thermoset Membranes

These materials are ones that chemically crosslink. What that means to you is that once seams cure you have one giant molecule of roofing over your head and possessions. That is a huge advantage. Many of the synthetic rubber roofs (EPDM) fall into this category. You also find the CSPE, CR, and ECR compounds/membranes in this group. These membranes are fairly thick and often you will find them in thicknesses between 30 and 60 mils. These roofing materials offer superior performance over a wide range of exposures. If applied according to manufacturers recommendations, they will give you leak free performance for many, many years.

Thermoplastic Membranes

These membranes are very similar to the Thermosets but there is no chemical cross-linking or vulcanization. Seams in the materials are welded together with solvents or heat. The welds - when done properly - are as strong as the material.
PVC plastic materials are part of this group as well as the following materials: CPA, CPE, EIP, NBP, PIB, and TPO. These are "code" acronyms you might hear the roofer talk about. Be sure to ask exactly what type of material you are getting so you can see which group it falls into!

Modified Bitumen Membranes

These membranes combine asphalt with modifiers and reinforcement materials. They are often a "sandwiched" roofing material. These materials can perform well in my opinion but they are not as advanced as the other two groups. These materials are often referred to as "torch-down" roofs because a large flame throwing torch melts the asphalt so that seams can be joined together. You might hear your roofer mention the names APP or SBS when referring to this membrane.

Roofing Membrane and EPDM Roofing Manufacturers

By Tim Carter
©1993-2008 Tim Carter

Summary: Membrane and EPDM roofing manufacturers are listed. The technical side of epdm roofing and membrane roofing info is covered for the roofer. You may prefer to contact these companies to locate local distributors of epdm roof repair products and roof membrane.

Major Players in Membranes

The following companies are the major players in the EPDM and membrane roofing. You can call them for information about their products, however it may be a waste of time. Why? This market is really geared to the professional roofing contractor, and NOT to the consumer. The information you will receive may be quite technical and dry. I can assure you it will contain language that is very chemically oriented. The better choice may be just to ask for local roofing suppliers who sell the products. Contact your local distributor for easier to understand facts and costs.

Carlisle SynTec
Firestone Building Products
RoofTop
Sta-Fast Roofing Products

Roofing Membrane Manufacturers

By Tim Carter
©1993-2008 Tim Carter

Summary: Roofing membranes are modified asphalt on sheeting and all virtually the same. Except for the thickness. Some of the roof membranes are produced for certain parts of the country as well. Buy the thickest membrane you can muster and take time to read product literature..it will pay off!

Wind Blown Rain & Ice Dam Roofing Membrane Manufacturers

All of the roof membranes are virtually the same. There are differences in the thickness of the modified asphalt. It can be significant. Some products are 25 mils thick while others can be 40 mils or more. To further confound you, some products are made for different parts of the country. Not every membrane can be installed in the desert Southwest for example. Some cannot be applied to metal roofing or beneath metal roofing. Some thinner ones do not protect against severe ice damming situations.

If you are doing the roofing yourself, another consideration comes into play. The plastic cover sheet can be slippery! Some membranes have special skid resistant surfaces. Look for those so you don't fall!

Sunlight can cause real problems with some membranes. This I don't understand. Don't ask me why the manufacturers can't employ decent ultraviolet blocking ingredients in all of their plastic cover sheets. Some products can be exposed to sunlight for only several days while others can be exposed for several months. It just doesn't make sense to me!

My recommendation to you is to go with as thick a material as you can afford. The more asphalt, the more protection you have around the nail shanks. Check out the following manufacturers and read their product literature. Invest the time reading it, and you will reap HUGE dividends.

ALCO-NVC
Certainteed
WinterGuard
GAF Building Materials
Weather Watch Ice & Water Barrier
Grace Construction Products, Inc.
Grace Ice & Water Shield TM
Johns Manville
Sure Grip
NEI
Tamko

Roofing membrane

Document Type and Number:

United States Patent 5981030

Link to this page:

http://www.freepatentsonline.com/5981030.html

Abstract:

A roofing membrane has a quantity of water-retaining particles fixed in the upper surface of the membrane. A fleece web affixed to the membrane surface in a quilt-like manner may provide zones of selectable size for holding the particles in place. By varying the amount of the absorber particles, the water-retaining capacity of the roofing membrane may be varied to the particular intended use, such as on a flat roof or a sloped roof.

Roofing foil Patent

Inventors:

Haupt, Bertram W. (Hamburg, DE)
Heinz, Siegfried (Berlin, DE)
Rudolf, Wolfgang (Berlin, DE)

Application Number:

08/936882

Filing Date:

09/25/1997

Publication Date:

11/09/1999

Assignee:

FAMOS GMBH (DE)

Primary Class:

428/143

Other Classes:

428/166, 428/15, 52/91.100, 428/72, 428/22, 428/137, 428/27, 428/913, 428/192, 428/178, 47/65.900, 428/198

International Classes:

D06N5/00; D06N7/00; E04D5/12; E04D11/00; E04D5/00; B32B7/04; E04D13/04; D06N5/00

Field of Search:

428/72, 428/166, 428/178, 428/143, 428/198, 428/192, 428/22, 428/27, 428/15, 428/913, 428/137, 52/91.1, 47/65.9

US Patent References:

3659396	May, 1972	Baker	53/180	SEED SHEETS
4534142	August, 1985	Drefahl	52/90	Roof covering
5287650	February, 1994	Moriguchi et al.	47/59	Structured medium for the cultivation of greenery and a waterproofing system to facilitate the installation of said medium on buildings
5309673	May, 1994	Stover et al.	47/59	Plant carrier
5410840	May, 1995	Loesken	47/58	Process for producing a support-free vegetation mat, particularly for roof greening
5456733	October, 1995	Hamilton, Jr.	47/58	Pelletized mulch composition and process for preparing same
5608989	March, 1997	Behrens	47/659	Plant growth system for the enhancement of the environment

Primary Examiner:

Watkins III, William P.

Attorney, Agent or Firm:

Oldham & Oldham Co., LPA

Claims:

What is claimed is:

1. A roofing foil, characterized by having a plurality of water retaining absorber particles on a top surface thereof, the absorber particles being arranged in fixed stable positions by means of a web which is applied as a laminated coating.

2. The roofing foil in accordance with claim 1, characterized by an edge strip on one side of the membrane which is substantially free of the absorber particles.

3. The roofing foil in accordance with claim 1, characterized by having a sufficient quantity of the absorber particles to provide the roofing membrane with a water retaining capacity in the range of from about 1 to about 5 l/m².

4. The roofing foil in accordance with claim 1, wherein the web is a water pervious fleece applied on said top surface.

5. The roofing foil in accordance with claim 4, wherein the fleece is fixed on the roofing membrane by a coating in the manner of a quilt and encloses absorber areas of variable size.

6. The roofing foil in accordance with claim 1, wherein is a perforated film which covers the absorber particles and which is applided over entire surface.

7. The roofing foil in accordance with claim 1, characterized by the fact that the absorber particles are applied directly onto the roofing membrane.

8. The roofing foil of claim 1 wherein the water retaining absorber particles comprise polyacrylamide.

9. The roofing foil of claim 1 wherein the plurality of water retaining absorber particles are evenly distributed over the entire top surface of the membrane.

10. The roofing membrane of claim 1 wherein substantially all of the absorber particles have a particle size equal to or less than about 1000 microns.

11. The roofing membrane of claim 5, wherein an edge strip on one side of the membrane is substantially free of the absorber particles.

12. The roofing membrane of claim 5, wherein there is a sufficient quantity of the absorber particles to provide the roofing membrane with a water retaining capacity in the range of from about 1 to about 5 l/m².

13. The roofing membrane of claim 6, wherein an edge strip on one side of the membrane is substantially free of the absorber particles.

14. The roofing membrane of claim 6, wherein there is a sufficient quantity of the absorber particles to provide the roofing membrane with a water retaining capacity in the range of from about 1 to about 5 l/m².

15. A roofing system, comprising:

a root impenetrable membrane, having a bottom surface and a top surface; and

a web which is applied as a laminated coating to the top surface, said web containing a plurality of water retaining absorber particles arranged in fixed stable positions.

DESCRIPTION

The invention relates to a roofing membrane which consists of a roofing membrane which cannot be pierced by roots as the base material and absorbers for water retention arranged on this base, held in a stable manner on the roofing membrane by means of a web coating.

BACKGROUND OF THE ART

It is known that absorber particles e.g. hydrophilic acrylamide polymers, are added to soil for the purpose of water retention in sandy soils, in order to reduce the quantity or water which sinks to a level beyond the reach of roots.

Similarly for retention, suitable gel granulates are added to various substrates used for grass covering of roofs to ensure sufficient water supply for the plants despite a relatively small volume of substrate (e.g. EP 369062).

However, freely mixing absorbers into vegetation substrates does not allow fixing of the absorber particles at a defined level in the substrate layer. Because the absorber particles wander, they become irregularly distributed in the substrate which has a negative effect on the retention capacity. Simultaneously, the volume alteration resulting from the absorption of water results in repeated shifting of the substrate particles within the vegetation structure and thus causes damage to the capillary root system. The shifting of the absorber particles can also impair the local stability of the vegetation substrate.

SUMMARY OF THE INVENTION

The current invention is thus designed in response to the requirement to create a root-impenetrable roofing membrane which has water retaining properties without possessing the disadvantageous effects involved when using non-fixed absorber particles. The water retaining roofing membrane is designed both for sloping and flat roofs and should allow an essentially constant retention and release of moisture which promotes plant growth. Additionally, the draining behavior of extensive roof greening projects with a small layer thickness should be positively influenced by this water retaining roof protection membrane, because the draining coefficient is kept low.

This task of the invention is resolved by the fact that the root-impenetrable roofing membrane serves as a direct base material for the moisture absorber. The absorber is fixed to the roofing membrane by means of a web which is water penetrable and attached to the roofing membrane. This fixing means that the absorber is not flushed out in heavy rainfall and also prevents it from wandering into higher levels of the substrate or shifting to the edges on sloping roofs. The advantage of this solution lies in the fact that the moisture absorber can be applied in a pre-determined distribution and dosage and the fixing ensures that the desired positioning of the absorber is maintained. The fixing of the web in accordance with the invention allows unimpeded water absorption and expansion of the absorber, Using a fleece-type web means that saturation of the gel particles with fine-grain substrate fractions is prevented, giving the roofing membrane a certain drainage effect in addition to its water retaining function, and simultaneously reducing unwanted excess water. Used in dry regions this roofing membrane ensures an efficient utilization of the low level of precipitation due to the surface-remote position of the absorber particles and the resulting low evaporation coefficient, so that a high quality roof vegetation is also possible in such areas.

Another advantage is the reduction of additional roof burden from the build-up of the vegetation when this water retaining roofing membrane is used, because roof structures with a few layers and very low layer heights can be used without detrimental effects on the vegetation and thus the function of the roof greening system. Equally advantageous is the option of varying the retention volume of the roofing membrane in accordance with the invention by employing suitable absorber distribution and concentration for different types of use (flat or sloping roofs).

A further version of the invention uses a water pervious web for fixing the absorber particles which is applied to the membrane in the manner of a quilt. When a roofing membrane manufactured in such a way is used, which can be used on more steeply inclines roofs, it is possible to adjust the size of the areas formed by the quilt-type coating to suit different requirements. In this way it is possible on sloping roofs to use membranes with a higher water retention capacity near the ridge than on the rest of the roof surface.

A further version of the invention takes account of the fact that it can be expedient for use of flat roofs to fix the absorber particles by means of a fully laminated perforated film. By using an adequately perforated film the unimpeded contact of water with the absorber particles is ensured. The volume increase of the absorber particles which results from the water absorption quickly causes the necessary lifting of the film from the base material, thus creating sufficient volume for the full utilization of the water retention capacity.

It is also possible to apply absorber particles with a particle size of ≥2 1000 μm in small quantities directly onto the membrane surface without any further fixing.

It is possible to use bituminous root-impenetrable roofing membrane as well as corresponding root-impenetrable membranes based on synthetic films as the base material for the absorber particles and the coating in accordance with the invention. The application of the absorber particles and the coating with the web are carried out while the base material is still in a plastic condition. The fixing of the web can be varied by using differently designed pressure rollers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is more closely described with the help of the figures.

They show the following:

FIG. 1: a top view of a roofing membrane with quilt-type laminated fleece

FIG. 2: a cross section of a roofing membrane with laminated fleece and absorber particles

FIG. 3: a cross section of a root-impervious bituminous roof membrane with details of the layer structure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the quilt-type lamination (2) of the fleece with which the absorber particles are fixed on the roofing membrane. The areas (6) in which the absorber particles are held in a stable manner and which offer sufficient space for the volume increase of the absorber particles, can be infinitely varied in size and shape (3) shows an edge strip free of absorber particles for the purpose of adhering the strips of roofing membrane together.

FIG. 2 shows a schematic cross section of a roofing membrane in accordance with the invention. The absorber (4) is applied in a defined dosage on the base material (5), which can be either a plastic film or a bituminous roofing membrane. The absorber (4) is expediently applied in a quantity which corresponds to a water storing capacity of 1-5 l/m ². The fleece (1) is firmly joined to the base material at predetermined intervals by means of lamination (2).

FIG. 3 shows a cross sectional detail of the roofing membrane in accordance with the invention shown in FIG. 2 on the basis of a bituminous root-impervious membrane. The build-up shows the fleece (1) with the laminated area (2) used for fixing the absorber particles (4). The laminated area expediently has a width of 10 to 30 mm. The bitumen membrane itself consists of two APP or SBS modified layers of bitumen (5a) and a combination insert (5b) which provides firmness and dimensional stability. The root-imperviousness of the membrane is achieved either with a Cu film in (5b) and/or with the addition of "Preventol" in (5a).

In a further version of the invention which is not represented in a diagram, the welding film (5c) can be applied in a highly perforated form on the top as a fixing aid for the absorber particles.