Serious trouble with 10 degree pitch roof on extension

hoody

Hi all, we've just added a one room extension to our semi-d. We're having a saga with the roof.

The pitch on the roof is at most 10 degrees, however neither the builder, the engineer or ourselves copped this until we started to see leaks appear once the roof was finished. The plans drawn up by the engineer make no mention of any consideration being given to the pitch of the roof. I have zero knowledge of building.

The roof has 2 Fakro windows which are specified for minimum 15 degree pitch. A standard tile was originally used which was specified for a minimum 17.5 degree pitch. Following the first leaks the tiles have been replaced with Gusclad however we are still getting a leak, albeit a smaller one.

Our options at this stage, as we understand it, are to remove the windows entirely and simply have a gusclad roof, which would lose us a lot of light in the room and the kitchen but is probably better for full leak proofing. Alternatively we sit the windows into a frame to increase the pitch they sit at but the fitting of the flashing around the frames would need to be of a much greater quality than we've seen so far.

Any help / advice would be greatly appreciated. Are we mad to still want to keep the windows given the trouble we've had so far?

Calahonda52

Is the issue with the window flashing or the roof, post hard to follow ITR.
If its a flashing issue get some of this stuff

-snip-

SC024

Fibreglass the roof will enable you to keep windows

Squall Leonhart

It beggars belief that the pitch of the roof was given no consideration by the designer, in this case your engineer.

hoody

Squall Leonhart wrote: »

It beggars belief that the pitch of the roof was given no consideration by the designer, in this case your engineer.

Yes it does! It's been a saga. Having had a couple of calls this evening we think we have a plan to get it right, a fair bit of work to be done on it yet but hopefully we can keep the rooflights and lose the unplanned water feature!

antiskeptic

hoody wrote: »

Yes it does! It's been a saga. Having had a couple of calls this evening we think we have a plan to get it right, a fair bit of work to be done on it yet but hopefully we can keep the rooflights and lose the unplanned water feature!

The problem (in my experience/12 degree roof) with the Fakro at a low angle isn't so much the window itself* or the side/top flashings but the bottom flashing (the one that runs across the bottom of the frame.

The bottom flashing is a piece of aluminium sheet formed to fit the window frame and has an apron on it - this apron is meant to span from window frame on down and over the roof tiles fitted a little distance away below. But the apron is very short (in the roof slope direction).

Because the apron is so short, the roof tiles directly under the window have to be set quite near to the window so that the apron can reach and be laid over them. There's a self-adhesive band on the underside of the apron to stick it to the top of the tiles it overlays.

Problem: because the tiles are so close to the window frame (and because they are thick and because you've a low pitch), there isn't much of a height difference between the valley of the wiggly shaped tile (where the water flows down) and the bottom of the window frame above them.

It's very hard to ensure you have a fall at all in the apron when fitted, let alone a fall of 10 degrees. Try and move the tiles downward in order to increase the fall and you begin to lose overlap of apron on tile - because the apron is so short.

Unless careful (and with builders not appreciating things), you end up with an apron that is nearer horizontal than anything else. In my case, the builder actually managed to form a U between bottom of window frame and the roof tile directly below (and I don't mean the peaks of the roof tile, I mean the valleys of the tile, via which the water is supposed to roll downhill). Naturally, the build up of water in the U simply poured over the side edges of the bottom flashing and into the house.

In my case I managed to adjust the apron/tiles to achieve an even fall (some wood under the apron to maintain it's flat shape and prevent a U being formed helped), no U's and a decent overlap. I also adjusted the sides of the flashing (bent them up, they are flat out of the box) to stop the tendency for water blown sideways over the bottom flashing coming over the sides. It's seen a storm or two since and is south-west facing (into the rain) and hasn't leaked.

-

You have a further problem will spells more overall trouble. Why isn't your membrane (your secondary "roof") doing the business? If properly fitted around the windows you shouldn't be getting water in, even if the primary roof isn't doing what it should. These membranes, though tough, often get damaged during a build (I've seen a builder propose duct taping ripped membrane) and detailing around the interface with rooflights is often appalling - they simply cut a hole out and pay no heed to detailing the membrane into the window before laying the roof tiles on top. "Ah shure, my roofs never leak - you don't really need the membrane" was one response I got to shambolic roof membrane fitment. But if you get anything water blown up under the tiles upstream of the window, it will come into the house via the lack of detailing around the rooflight.

I gather Velux do a longer apron than Fakro, which might be one way around the problem. Probably for this self same reason.


-

By putting on a thinner roofing, you can expect to alleviate the problem somewhat (you've not got thick roof tiles > the roof you've to lay the apron on is lower wrt the window frame> and so the fall of the apron increases. But it sounds like the same same fundamental problem ... remains.


* Fakro at low angle aren't as tolerant to window opening angles as Velux. The rain drips in at far smaller angles of opening with fakro than Velux.

SC024

Squall Leonhart wrote: »

It beggars belief that the pitch of the roof was given no consideration by the designer, in this case your engineer.

+ the lad that done it.

antiskeptic

hoody wrote: »

The sketch drawn on the back of a cigarette packet by the (sanitation?) engineer make no mention of any consideration being given to the pitch of the roof.

Fixed that for you

I have zero knowledge of building.

You asked for advice from somewhat informed randomers on a discussion forum. It seems you have a tad more knowledge about building that your engineer.

BryanF

Did eng spec fakro?

Meningate

If you change the roof covering from tile to slate and change the window flashings from tile flashings to slate flashings you should get away with it. Even so it's a ridiculous angle. Another option would be to board it and felt with green mineral surface torch on top layer onver a black base layer. The Windows should be able to be sealed completely with this. Good luck.

antiskeptic

Meningate wrote: »

If you change the roof covering from tile to slate and change the window flashings from tile flashings to slate flashings you should get away with it.

I would have thought the opposite would be the case: a tile won't lend itself to capillary action like a slate will.

Whatever the case, a precise understanding of where and why the leak is the first step to take. It will inform the nature of the remedial action (which might not involve something as drastic as reroofing the whole roof)

sydthebeat

Meningate wrote: »

If you change the roof covering from tile to slate and change the window flashings from tile flashings to slate flashings you should get away with it. Even so it's a ridiculous angle. Another option would be to board it and felt with green mineral surface torch on top layer onver a black base layer. The Windows should be able to be sealed completely with this. Good luck.

there is no slate thats certified for use at that angle