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How Often Do Flat Roofs Need Replacing?

When a flat roof needs to be replaced is determined by a number of factors which includes the roof’s exposure to the weather, the condition and age of the roofing materials as well as the construction of the roof. However, with proper maintenance and regular inspection, they should be used for nothing less than 50 years. There are some commonly used types of flat roofs which includes Felt flat roof as well as a GRP flat roof.

Felt Flat Roof

The lifespan of a felt flat roof also varies depending on the quality and grade of the felt roof incorporated. This can make the roof last within the range of 2 to 20 years. More often than not, felt flat roofs are usually installed in such a way to keep the costs down which implies the grades of felts that are mostly used are the economical ones implying a very short lifespan.

In the event whereby a premium grade of felt is incorporated in constructing a roof by professional contractors, will be guaranteed by the manufacturer to last between 10 to 20 years.

One of the major causes of a short lifespan in felts is leaks which should be regularly inspected and repaired once identified. If not, the roof will gradually deteriorate and become a lot weaker due to the action of the sun. However, when a felt roof starts to leak, it’s usually a sign that’s approaching the end of its lifespan and a replacement should be taken into account.

GRP Flat Roof

The GRP flat roof or fibreglass flat roof usually comes with a manufacturer’s guarantee of 20 years and is expected to have a lifespan of a minimum of an additional 10 years.

Unlike felt roofs, they’re more resistant to leaks. However, they should also be regularly inspected for leaks which are caused mostly as a result of installation error rather than the GRP roofing approaching the end of its useful life. If the GRP roof repair does not totally resolve the leak, you should start considering a replacement.

Blisters are most common on membrane roofing systems. Lots of contractors will tell you that if there are no signs of further damage, there might not be any need to repair flat roof blisters. They form when pockets of air or water get trapped between layers of the roof’s membrane or between the membrane and the frame. When the sun is out and it heats the pockets expand and stretch the membrane. If you do want to repair your flat roof blisters, there are a few ways to go about it.

If you have a membrane flat roof, cut away the membrane until you reach a place where the membrane is still stuck tightly to the roof. Reapply as many new membrane layers as you cut away over the blistered area. You might even need to do more. To make sure your patch remains watertight, you’ll need to leave at least 6 inches around the edges of the blister.

If you’ve got a felt roof, you can cut an X shape through the blister. Peel back the triangles that you’ve made and let the timber frame dry for a while (so don’t do this when rain is forecast!). Then, coat the area with lots of bitumen adhesive and leave it to dry until it feels tacky. Then press down the triangles of felt firmly into the adhesive.

After that, you’ll need to add more bitumen adhesive to the cuts you made. If you’ve got any spare roofing felt, cut a square that’s about 100mm bigger than the cuts then lay this over the adhesive. If you’ve not got any felt, it’s cheaper to use a self-adhesive flashing strip. Once you’ve laid the strip or patch over, seal the edges with more bitumen adhesive.

Fitting a Velux window into a slate roof is very similar to the way you’d install it in other roof types. All roof windows, whether a Velux-branded one or not, will come with detailed instructions for you to follow if you want to have a go at fitting it yourself. But here are some brief instructions to give you an idea of what’s involved in installing a Velux window into a slate roof:

1. After you’ve removed the Velux window from its packaging, remove the sash (the part that opens) from the frame, according to the manufacturer’s instructions.
2. Next, you need to prepare the opening for the window. You can often cut through the felt, remove one of the battens from under a slate, then slide all the slate tiles into the roof space. You should then make the cut 40-60mm wider than the window, cutting away roof timbers then replacing them with more around the opening to strengthen it.
3. The roof window’s bottom brackets need to be installed on one of the existing battens for the slate roof. One of the slate courses should line up 105mm below the top edge of the batten you use.
4. Then, measure from the top edge of the batten upwards to the height of the window plus 45mm. This is where the top installation batten should be installed, with an overhang of 100mm on each side.
5. Remove the course of slates below the window, trim any excess felt and fold it over the surrounding timber. This helps with waterproofing.
6. Add the insulation collar according to the Velux window manufacturer’s instructions.
7. Place the frame in the opening, adding the brackets according to the instructions. You’ll find that lots of roof windows have pre-drilled holes to make it easy for you.
8. Replace the sash and line up the hinges. Take a look at the opening at the bottom between the sash and the frame – it should be even along the entire width. Remove the sash again to fix the upper brackets according to instructions.
9. Add the underfelt collar for your roof window as instructed by the manufacturer, then replace any slates at the bottom. You might need to cut them to size.
10. Next, add the flashing according to the instructions, along with any parts that are not yet attached, including the hood section and top flashing piece.
11. Replace all the slates around the window, allowing 60-100mm of space between the course of slates above the window and the top of the window to allow for rainwater drainage. Then replace the sash into the frame again.
12. Add the vapour barrier on the inside of the window using the screws provided, then tape it to the existing vapour barrier to prevent moisture from reaching your roof structure.

And that’s it! If you think that sounds a bit complicated, ask a roofer or window installer to fit your roof window into a slate roof for you. You’ll get a better finish and you can be sure that you won’t get any leaks from a botched installation.

How To Replace Flat Roof Felt

Also referred to as tar paper, roofing felt is installed underneath the roof’s shingles to help deny water access to your home. Installing the roofing felt in overlapping layers builds a water barrier in situations whereby the weather damages or blows away the shingles. Although the application of a roofing felt on a flat roof is relatively easier and safer than working on a peaked roof, it’s advisable to take enough care and precautions. If you lack proper training and experience for this task, we’d recommend you employ a reliable professional to guarantee the best results and save you from further headaches especially in cases whereby unfortunate errors are made. This step by step guide will give you a good insight into the flat roof felt replacement process.

• Take a measurement of the width and length of the roof.

• Calculate the square footage by multiplying the numbers.

• Multiply the square footage gotten by three (it’s advisable to install three layers of roofing felt to create a really strong weather barrier).

• Use a claw hammer to remove the existing roofing felt.

• Use utility knife to cut the new felt to fit the length of the roof.

• Place the first piece along the roof’s edge and use a hammer tacker to tack the felt in place with staples or galvanized nails and hammer.

• Put the staples or nails at every 6 inches along the side touching the roof’s edge as well as down the short sides.

• Repeat the same process for the second piece, laying it out beside the first row of felt.

• Cut a piece of felt to the appropriate length using a utility knife to begin the second layer of roofing felt, and cutting it in half, lengthwise.

• Apply construction adhesive along the first row using a trowel.

• Press the first piece for the second layer onto the adhesive. Repeat this process until the roof is covered with a second layer

• Apply construction adhesive over the second layer to install the third layer. Begin with a full piece of felt without cutting it in half.

• Overlap each piece by 2 inches until you’ve completely installed the third layer.

Commercial roofing simply refers to any roofing work, including installation and repair, that is done to commercial buildings. This might include office roofs, shop roofs or commercial unit roofs. Every building needs a roof to keep out the rain!

Since looks aren’t usually the first priority with commercial buildings, lots of commercial properties have flat roofs. These are often made from felt, EDPM rubber or fibreglass. Felt is the cheapest commercial roofing material, while fibreglass tends to be the most expensive. In felt roofs, roofers use an adhesive to stick roofing felt onto a frame. EDPM rubber roofs have a rubber membrane that is laid down and glued onto the roof and coated with a contact adhesive, while fibreglass uses a cut glass fibre mat that is pressed on before a resin and topcoat are applied.

Not all roofing companies will offer commercial roofing services, because generally the buildings tend to be bigger. Small companies won’t have enough tradespeople to work on a roof without making it very expensive for you. Commercial buildings also tend to need more scaffolding to make it safe for the professionals to work, so some smaller roofing companies won’t offer commercial services. Make sure you check a company’s website or social media if you’re looking for commercial roofing – on the Quotatis Directory, our roofers will show whether they do commercial roofing to make your search easier.

If your existing roof is still in good condition but the membrane is getting old, it’s often not worth exposing the structure to the weather whilst the contractor strips off the old membranes. The contractor will leave them in place to act as a base layer for a new roofing system. As long as there are no other problems with your roof, then overlaying is a good way to replace your flat roof.If you have any more questions about flat roofing that aren’t listed here, fill out our form to ask a contractor.

Whether you’re liable for a leaking roof in a commercial property will depend on your ownership status and any contracts. Of course, if you own a standalone commercial property, it would make it your responsibility to repair to leaking roof. But if you own an office within a building, you should check your paperwork to see whether you are responsible for some or all of a leaking roof.

If you’re a tenant in a commercial property, things get a bit more complicated. Lots of commercial leases are FRI, or Full Repairing and Insuring leases, which means that the tenant is responsible for all external and internal maintenance and insuring the building. It means that it’s vital that you read through your tenancy agreement in full before signing it and seek legal advice if you think you need it. If your lease is an FRI lease, you are liable for a leaking roof in your commercial property.

It’s important to ensure that you have a schedule of condition for the property, which will mean that you only have to restore the commercial property back to the condition that it was in when you took over. It’s also worth getting the roof inspected before you sign the lease, as if there is any damage before you sign the landlord may be responsible.

The best way to avoid having to pay for a leaking roof in a commercial property is prevention. If you are liable for repairs and maintenance, make sure you have the roof inspected regularly by a reputable company to avoid having to pay for costly repairs when disaster strikes.