Pitched roof extension, tiling issues

19 Jul 2014
Reaction score
United Kingdom
My builder hasn't tiled the sections of our new pitched roof extension that sit beneath the windows of the existing house. He said the pitch of the roof would not allow for tiles and flashing so we're left with what I presume is the membrane exposed. Is this normal or will it result in leaks in years to come?

Sponsored Links
The flat roofs below the windows have been finished in mineral cap sheet!
The detailing at the verges and tiling look very untidy.
As above.
The untidy tiling appears to have run into trouble between the Velux frames - has it lost its bonding? And whats happened where the tile meets the main house wall - one gigantic leap disguised by a wide cover flashing?

You will have leaks in no time, and when winter snow builds up, the water will pour in - surely BCO hasn't approved of any initial drawing or the work in-situ?

You could strip the upper tile down to the change of pitch/lead flashing line. And then re-lay new tile across the roof, in a tile designed for the low pitch from below the cills to a continuous flashing line where the pitch would change. google pics for Mansard roof.
As above.

You will have leaks in no time, and when winter snow builds up, the water will pour in - surely BCO hasn't approved of any initial drawing or the work in-situ?

What did BC say when they did their mandatory roof inspection? Surely it was obvious at that point that you were going to have this problem and it should have been pointed out. Did use an architect? Did he specify this construction? I assume you are building off a notice as opposed to full plan submission as this would surely have been questioned before a spade went in the ground. I wouldn't be happy with this and would want the roof redone properly at the expense of whoever is responsible for this clanger. If this is not possible then you have a couple of options to try to prevent ingress.

The cheapest option would be to address the problem specifically beneath the windows. You already have water pooling on there, this is bad, especially when it freezes and thaws. You must redo this so it incorporates the maximum fall you can achieve. Remove the felt and use finings or wedges to get your fall then board and membrane, flashed properly where possible and whatever you can achieve under the window sill, flashing tape, silicone etc.
you need eaves protection on each of the 'gable ends' around your windows just as you do on the eaves of your extension, you could frame it and use cement board under your tiles for a mortar bed and UPvc cladding at the sides with your membrane flashing under the cladding.

Another option is to do away entirely with the roof where the pitch ends and have it done as a flat roof from that point, membrane, flashing etc.

Replacing your upstairs windows, adding a couple of courses of bricks to raise your sill height is an option...

It's hard to tell how much lap you have on your flashing at your transition but it doesn't appear to be enough, perhaps get this checked?

As I said at the start I wouldn't be happy with any of those options and would have the entire roof redone, the pitch you will be left with may be too shallow for tiles, I don't know, in which case a major rethink is in order.

Also, it might be my eyes but do you have engineering bricks up to dpc?

Hope this helps, I'm sure I've missed a few things but it might point you in the right direction.

Sponsored Links
Thanks for all your comments. The builder did say that the tiles between the velux windows had to be sloped inwards, to allow water to drain away from the frames. In terms of the wall construction, I can confirm that engineering bricks were used, up to DPC.

BC have done their initial inspection but admitted that they only looked at the internal section of the roof and would take a look at the external work as part of their next inspection.

We were originally going to have a 3m wide structure, with a full pitched roof and instructed a draughtsman to produce drawings accordingly, we didn’t use an architect. We then decided to increase the width of the extension to 3m internally, bringing the overall structure to 3.5m. Drawings were amended, submitted to planning and we received permission. It has only just been pointed out to me that a fully pitched roof cannot not be achieved on a 3.5m structure but our draughtsman failed to highlight this on the revised drawings. Therefore the builder has had to install a flat roof protruding 0.5m from the house, before sloping it down to a 15’ pitch.

I will suggest that the contractor do as Ree suggests and if that’s not possible, remove the felt and install wedges to get the required fall, as Jason1970 suggested.

One more question, 3 centre pivot veluxs have been fitted but I’m concerned that if there is rain water sitting on them when opened, it will fall into the room below. Wouldn’t top hung veluxs be a better option, so as to avoid this risk?
Ideally the simplest solution would be to do it in lead though the fall needs addressing as its pooling at present and a lead worker needs to be employed to do it not your butcher, ahem builder! However that said this may not work either as we don’t know the height from the flat bit to the cill, presumably FA! Some more photos looking towards the windows would be helpful. I wouldn’t rely on BC reprimanding the builder, they may do but maybe not.

Who’s to blame?

The draftsman should have addressed and should have drawn a practical solution so him to start with though we don’t know what you paid for the drawings. The builder should have realised this was going to happen when he started fitting the rafters if not earlier so he must also share some blame. Though you may have to keep it friendly with your builder as you want him to put it right.

With regards to the draftsman I would write a nasty letter to him saying he should inform his PI insurance supplier as he can expect a nasty letter from your solicitor and will need to make a claim, even if you have no intention of doing so, it will be guaranteed to give him some sleepless nights whether he has PI or not!

Using a draftsman and not an architect is a red herring, many draftsman are good and many architects are rubbish. As ever though when will people realise that building from crap planning drawings is a false economy.

One things for sure, it’s a complete cock up that will leak like a sieve unless addressed soon.
What i suggested is perfectly possible but will require demolishing the upper pitched roof areas and rebuilding a new pitched roof to whatever falls are avilable.

As above, it could be done in lead (but think cost and theft), synthetic cap sheets or tiles suitable for that pitch.

All thats needed is someone to pay for it - if you attempt to codge this in you will be paying much more down the road.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links