Flat Roofing Systems

  • 10-3-10

If you give your roof a little care and attention and replace before it lets you down and use a High Performance felt then you will have many many years of piece of mind.

I am also registered with and fit RESTRIX EPDM single ply systems, which out of all the single ply sytems I am happy to install, please look up under SINGLE PLY EPDM SYSTEMS on this site.

Each system has it downfalls in some shape or form, and with felt roofs it was cheap felt before the advent of polyester felts this has all now changed.


High performance specifications are now always recommended for built-up roofing and should completely displace lesser specifications from the market.

Most high performance felts are made on a polyester fibre base which is more than strong enough for roofing purposes, and has a high elongation at break which exceeds all demands likely to be met in service. Past problems with built-up roofing, before the use of polyester, were almost all concerned with splitting of the membrane due to an inherent lack of strength. Such splitting is now a thing of the past, and split polyester base roofing specifications are practically unknown.

Polyester roofing has been in regular service for some 25 years and there appears to be no report of failure through ageing. Reported defects have been due to design faults or workmanship faults, for example at outlets or pipes Polyester felts were originally made with oxidised. bitumen coatings, but the majority are now made with modified bitumen coatings. These have further improved performance under test, and have improved handling characteristics on site, particularly in cold weather

The polyester itself is manufactured in one of two different methods which produce materials with differing characteristics. Needled polyester forms a relatively thick material with an open structure. Spun bonded material is more densely compacted, and tends to be stiffer and stronger. Both forms of polyester are equally suitable and roofing manufacturers make a choice to best suit there own process and economies and achieve a good balance of handling characteristics and performance on test. Relatively recent developments have included the introduction of polyester bases reinforced with glass fibre scrims to improve dimensional stability and tear resistance. Also laminates of polyester bases with glass fibre tissues and with aluminium foil to improve fire resistance. The addition of a polymer to the bitumen improves its properties as a roofing material in almost all respects, and in particular the flexibility, strength and fatigue resistance. Polymer modified bitumens are usually applied to a base of polyester or glass. The most commonly used modifying additives are SBS (styrene butadiene styrene) and APP (atactic polypropylene).

The addition of SBS to bitumen makes the bitumen more rubber like. The finished roofing material is more flexible at low temperatures, with greater elasticity than those manufactured from oxidised bitumen. The softening point of SBS modified bitumens is in the order of 110C. Felts using SBS modified bitumen can be manufactured for application either by bonding in hot bitumen or by torching, depending on manufacturers recommendations. Adding APP to bitumen greatly improves its high temperature performance, enhances its flexibility at low temperature, and can give improved weathering characteristics. The softening point of APP modified bitumens is approximately 150C. An effect of this high softening point is that hot bitumen used on sites to bond felts is not hot enough to melt and fuse the APP modified bitumen, and therefore these materials are not suitable for bonding in hot bitumen. They are primarily for application by torch.


Are you currently getting quotes for the refurbishment / repair of a flat roof?

You may not really be getting comparable quotes, and you may be facing difficulties further down the road if the quote you have doesn't take the following information into account.

The revision (from 2002) of Approved Document L of the Building Regulations (Conservation of Fuel and Power) actually came into force in April 2006. The idea behind the revision was to help implement the Energy Performance of Buildings Directive / EPBD of trying to reduce the energy used in building (relative to the pre-revised directive) by between 20% and 28%.


How does this effect my flat roof repair and refurbishment?

The revision of the building regulations means that when a flat roof is being refurbished, there may need to be some work carried out on the insulation of that roof. The U-Value of roof insulation is a figure that represents how well it conducts heat, and the revised regulations have a target U-Value of 0.25 for existing buildings, and 0.20 for new builds. This means that if your flat roof insulation doesn't match up to or exceed this U-Value figure, when your flat roof is repaired, work will need to be carried out in the insulation to make sure that it does comply. If there was no insulation, it will have to be added, and again should comply with the U-Value figure. There is obviously likely to be an extra cost implication here. If your roofing contractor however doesn't take into account the likely cost of insulation work in the figure for your flat roof refurbishment quote, you are not only receiving an essentially inaccurately low quote, but there could be other implications:

The roofing contractor may not be aware of the revised Building Regulation, or worse.. The roofing contractor may not or carry out the extra insulation work.


For more details, enquiries about exemptions, and for general help and information on this, contact you Local authority Building Control Office


Tips on Locating Flat Roof Leaks

Safety first, always secure ladders. Make sure that the decking has not failed as this will not allow you to walk over as it might collapse, if the decking has rotted use suitable boards spread across the main rafters. If the decking has failed over a large area, then you will need the roof stripped and re-decked and re-felted, making repairs impossible

Flat roof leak roofs can be hard to locate. The reason is that water can enter one spot and not really express itself inside until it is far away from the leak. The same thing can happen on a sloped roof, however, you can usually discount all the roof area below the area where you see the leak. Why? Because water doesn't generally flow uphill from the leak location. Flat roofs allow the leak to travel in any direction from the leak point. That is why they are tough to locate.......

Start With a Dry Roof

If you have a flat roof that leaks, get up on it when it is dry and cool. You want to look for trouble spots that generally are the primary source of leaks.

I always start at flashings. Flashings are transitional roofing materials. A flashing connects a roofing membrane to something that is not a roof. For example, If a plumbing stack or chimney pops up through the roof, it will be surrounded by a flashing. Often the flashing materials are metal. Look for cracks. Look to see if the flashing overlaps the roofing material such that downward falling water will be deflected away from the chimney, wall or plumbing pipe.

Check the edge of the roof. Often flashings are used at these points as well. See if they are secure. Look for little cracks, openings, or breaks in seams in these flashings.

Often water will pond in low spots in a flat roof. You will see evidence of these areas on a flat roof. Look for concentric rings of dirt as the puddles dry out. Look here for tiny holes or splits in the roof.

Seams - A High Priority

Any seam in the roofing material is a natural spot for a leak. Look closely at all seams. Do you see cracks or holes of any type? Is there a place where you can lift a small edge of a seam?

Testing For Leaks

You can test for leaks using a hose. But you have to be patient and you need to work backwards away from gutters or centre drains. It can take hours as you need to let the water run slowly over areas you think are trouble spots. Remember, it can take 10 minutes or more for the water to begin dripping inside. Start near a drain and let the water slowly run. Periodically adjust the hose so water flows across dry portions of the roof. You will need tremendous patience, especially if all portions of the roof appear tight.

Any repair should give you time to call out a roofing contractor who can quote and arrange a date for the main works to be undertaken. Do not expect any repair to last for any length of time, it will let you down at the worst possible time.

We do not recommend any repair as this normally means the felting has came to the end of its life and will need replacement. S.F. roofing will not normally undertake any repairs for this reason, unless its a new damaged roof etc. We of course will visit and give you a full no obligation quote.


We prefer and strongly advise using 18mm O.S.B. Grade 3 boards within our specifications, as do most roofing bodies.

There has been a lot of problems with regards to cheap imported boards over the last several years. Laminating is one major concern, there are others, but with O.S.B. garade 3 boards at least you know that they have been made for this purpose.

One thing I come up against when pricing is that some customers are asking if I use Marine ply, NO I do not as there really is no need when you have boards made for flat-roofing. Another thing is that customers are being told by some companys that they use marine ply and then fit standard ply. Marine ply is very expensive but to some traders a good selling point, fine if they are going to use them, mostly do not. Again there really is no need O.S.B. Grade 3 is advised by many bodies.

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