1. Poor craftsmanship

Installing flat roof coverings, be they felt, asphalt or sheet metal is a specialised job. A number of the issues related to felt coverings to flat rooves come from bad craftsmanship. DIY felt jobs are the most significant culprit and are merely saving up issues for the future.

2. Ponding

‘ Flat’ roofings are not technically flat but have a minimum gradient of 1:40. Where the appropriate fall has actually not been integrated in or has been changed by structural motion ‘ponding’ is likely to occur i.e. rainwater choosing the surface. Where water is allowed to rest on the surface area of a felt roof for an extended period its life-span will be dramatically reduced.

Flat roofings that remain wet for long periods supply the perfect conditions for moss growth. Moss can assault the surface area of the felt and the moss itself serves as a sponge taking in water and causing further problems as it freezes and defrosts in winter season.

Peter Barry Surveyors carry out RICS Homebuyer Reports and Structure Surveys throughout North London including the popular locations of Muswell Hill N10, Crouch End N8 and Islington N1. We can generally take guidelines at short notice and reports are turned around within 2 working days.

3. Thermal Movement

A good quality solar reflective paint or a layer of light coloured chippings will decrease thermal motion and associated stresses to asphalt and felt roofing systems. Where the surface is not properly secured creasing will occur and ultimately lead to divides.

Sheet metal coverings such as lead and zinc have high coefficients of linear expansion and are therefore laid in little panels with overlaps referred to as ‘rolls’ or ‘seams’. It is necessary that coverings of this type are given space to broaden and agreement or it is inescapable that the product will split.

4. Blistering

This is a flaw that impacts developed up felt roofings. It happens when wetness ends up being trapped in between badly bonded layers of felt. When the water evaporates in to a gas and broadens it can not escape therefore forces the layer of felt above up to form a blister. The origin may be something as basic as the roofer not effectively protecting the felt from rain during the installation procedure.

5. Individuals

Throughout a warm summertime flat roofing systems become unlawful terraces and their asphalt or felt coverings go through point loads simply when they are most vulnerable. The result is a series of pot marks which allow moisture to ingress and trigger the covering to fail the following winter season.

One of the most typical causes of failure in sheet metal roofing systems is leaks triggered as an outcome of people (consisting of surveyors!) strolling on the surface area. It might be that the covering was laid on a surface area that was not totally devoid of grit which subsequently gets required through the covering when weight is applied from above. It may simply be a little piece of tile or slate that has fallen from a roof above which when walked on triggers a leak.


In my opinion, the most recent reinforced torch-on felts are the very best product for many domestic flat roofings. They are the modern equivalent of the traditional built-up felt roofing system covering, where the layers of felt were bedded in hot-poured tar or bitumen. The torch-on felts are applied in the same way, in layers, with the benefit that rather of needing to melt bitumen and pour it over the roof, the underside of the felt itself is softened with a blow-torch as it is presented. The accident at your neighbour’s home would most likely be triggered by reckless or inept workmanship instead of a fundamental danger at the same time.

It holds true that fibreglass and synthetic rubber membranes are being promoted as maintenance-free and more long lasting than felt. They are still reasonably untried, and the companies doing the work are often franchises of bigger companies, which indicates they may not be local, and may not be in business a number of years thus needs to problems occur. The 25-year “guarantees” provided for a few of these products are hardly ever worth the paper they are composed on, and the costs charged are typically much greater than for a traditional felt roof.

A properly-installed felt roofing system must last for 50 years or more, and has the advantage that if it were unintentionally damaged (by falling branches, for instance), it would be repairable by local tradespersons utilizing tried-and-tested strategies and materials.

The most crucial element for any flat roofing system is typically not the covering, but the underlying structure. Flat roofs must have a gradient of a minimum of 1-in-80 to make sure fast rainwater run-off, and timber roofing system joists need to be significant sufficient to withstand sagging with time, which can result in “ponding”, as this can permit water to find its way in as a result of the smallest pin-prick.

Another common cause of failure has actually been using chipboard as a decking product – this sags under its own weight with time, specifically when softened by condensation from below.

Regular readers will understand that I do not usually advise trade association membership as a mark of quality, but the roofing industry has a poor reputation, and it would be simply as well to use a member of the National Federation of Roof Specialists (020 7436 0387 www.nfrc.co.uk) or the Flat Roof Alliance (01444 440027 www.fra.org.uk), which also publishes a complimentary pamphlet, The Householder’s Overview of Flat Roofing


We have a 23-year-old felt flat roofing system on a first stage extension five metres square which is cracking and has to be changed. We do not dream of to have a “torch-on” felt roofing system (neighbours had their home burnt down by professionals doing that) and the options seem to be fibreglass or rubber. Is one of these naturally better than the other in terms of security of setup, durability and expense? The roof gets no foot traffic.


Q My flat roofing is dripping and has to be repaired. It has to do with 3m x 5m and is presently felt and tile building and construction. I have actually gotten a number of quotes from various companies, a few of whom seem eager to carry out the repair work utilizing EPDM rubber membrane. Is this suggested? Also, one professional has actually notified me that building controls use to the work and I need to employ a surveyor for pre-inspection and conclusion in order to get a certificate from the local authority. Is this appropriate? MS, by e-mail

A The main issue with flat-roof repair works is not usually selecting the product for the weatherproof covering, but identifying why it leaked in the very first place. Numerous British flat roofing systems are too flat and developed with inadequate structural materials, so they droop in the middle, permitting rainwater to pond, which then finds its way as a result of any pinprick imperfection.

A “flat” roofing needses to actually have a gradient of at least 1-in-80, to permit rainwater run-off, and have a decking of marine or WBP plywood. If your roof is shallower than this or decked with chipboard, then it doesn’t matter what you cover it with– it will ultimately leak once again.

Personally, I choose a “conventional” covering material, the present version of which is enhanced torch-on felt. Correctly used, it has a life expectancy of 50 years. EPDM rubber may or might not last this long– it hasn’t been utilized long enough to judge. Like fibreglass, it is typically used as a sticking-plaster solution on top of existing failed flat-roof coverings– which is asking for trouble, as discussed above.

The current Building Regulations dictate that any flat roofing being re-covered must at the same time be insulated to the current standard. This indicates you need to either alert your local authority’s building-control department to inspect and approve the work or use a roofing specialist registered with among the government’s “self-certification” schemes. Insulating a flat roofing system is clearly an excellent idea, but needs to be maded with care so as not to trigger problems with condensation and wood rot in the structure.

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The best option is typically to lay stiff foam insulation boards on top of the weatherproof covering, as this keeps the entire roofing system structure above dew-point temperature level. Paving pieces can be laid on top of the insulation as a weighting layer and to permit gain access to as a roofing garden. You describe your roof as being of “felt and tile building”, which sounds as though this might be a possibility in your case.

As I have mentioned frequently, subscription of a trade association in itself is not a warranty of good work, however in this instance I do suggest that readers use members of the Flat Roof Alliance (www.nfrc.co.uk/FRA.aspx; 020 7638 7663).

For even more information about flat roofing and the best flat roofing team in Salford and Manchester click on the link.