Flat roof replacement - your advice

[dmstewart]

Hi all,

We have an outbuilding with a flat roof, the flat roof felt was replaced just over two years ago but before we moved in.

As you will see from the pictures, water pools on top of the flat roof and you can see that its physically sagging down in the middle. This is obviously a bit of a concern and so we got some quotes on to fix/replace.

We've got three types of option and quotes and I'd very enormously grateful if you you could give advice on your preferred options - i.e. what would you do if this was your roof!

1) Add a beam down the middle of the roof (width ways) to raise the middle, leaving the original joists and board in place and essentially building on top of it then re-felt. Quotes come in at approx. £2000-2200. 10 year guarantee.

2) Replace the joists and boards and re-felt the roof. Quotes come in at approx. £3500. 10 year guarantee.

3) Replace the joists and boards and put a PVC membrane advanced flat roof solution in place (company called High-Tech membrane roofing). Approx £9000. Guaranteed for life.

The actual felt looks fine, unfortunately the work underneath and to ensure that the roof drains appropriately was not good. To me option one makes sense and the guy who reviewed it and quoted the work is very well thought of, but I'm not sure if I just like it because it's cheaper!

So any thoughts much appreciated, thank you.
Darren

 

[oddjob1200]

This sounds similar to the problem I had with my own roof. We added a beam and built on top effectively. This would ( in my opinion ) be the best and most cost effective way of going about it so long as what you are going on top of is sound. I installed Rubberall on our roof and we are delighted with the way it looks and how easy it was to do, especially when the guarantee that came with the material is for 30 years and the cost was as good if not better than almost anything else I came across. I hope it works out for you whatever you decide to do.

 

[ree]

Your best bet is to fix/strengthen the existing roof joists or, no matter what you build over the top, the joists will continue to sag.

If, whoever built the roof, couldn't get the joisting right then the odds are that there are other doubtful aspects of the build.

If the long back side of the roof is raised to fall and discharge into an accessible gutter on the front side it would keep it simple.

google pics of flat roof edge details.