Dormer flat roof to pitched roof ridge

[nealblath]

Hello guys, hoping you can help.

We have bought a bungalow to retire to and are converting the loft into a dormer bedroom/bathroom. We are doing most of the work ourselves as we have fully renovated 2 houses before.

We had plans drawn up by an architect and he designed the dormer roof to be a warm roof and the remaining pitched roof to be a warm roof too.

The architect has drawn the pitched roof and the flat roof to meet at the ridge as can be seen from the drawing attached.

He has specified that the pitched roof has a breathable membrane and counter battens to allow ventilation from the eaves to the ridge.

We were thinking of installing a dry ridge system to allow for this ventilation. However, how can we seal the dormer roof to the ridge using either a dry ridge system, or refitting the original concrete ridge tiles which has a ventilation duct on the middle ridge tile?

We will be covering the dormer with EPDM and was thinking of creating a little upstand of about 50mm under the ridge and creating an overlap of the EPDM over the ridge and overlapping the membrane under the pitched roof tiles, but want to make sure we don't ruin the ventilation path on the pitched roof side.

I’ve read that you cannot cement onto EPDM so was thinking of putting a layer of lead flashing between ridge tile and EPDM.

We have also to link the VCL of the dormer roof to the VCL on the underside of the pitched roof joists to maintain the vapour seal of the two roofs.

Any help would be appreciated, thanks

Proposed ridge detail.pdf

[Nickfromwales]

Would a parapet detail be more robust? Have you discussed this with the designer? 

[saveasteading]

Driven rain from the right is likely to breach that ridge. Increase the slope and  also totally seal the peak with either an upstand/parapet, or a continuous,  impenetrable roof surface.

[nealblath]

thanks for the replies lads

lease see below with what I was proposing to do

I asked architect and he more or less said ask a roofing contractor to sort it out

[saveasteading]

31 minutes ago, nealblath said:

ask a roofing contractor to sort it out

That is wise IFFFFF the contractor is knowledgeable. Lots are not, and get by because they are prepared to work at height.

Your detail looks fine as long as any joints in the lead are sealed... once water finds a way in, more follows. Seriously I think there must be capillary forces.

[Nickfromwales]

You need a better architect ffs !!!!!

[saveasteading]

32 minutes ago, Nickfromwales said:

You need a better architect

Otoh..   not bluffing.  Perhaps not a capital A one, but what used to  be called a draughts person..... they have all disappeared through title inflation, but I worked with some who were very expert on detail within their niche, and proudly so.

[Nickfromwales]

Architectural technicians seem far better value for money, and are usually sat behind the architect who’s fronting the show and commanding the money.

 

Some are just SERIOUSLY underwhelming and others just dire. 
 

Some very good ones out there too, of course, but you need to apply a lot of filters and do the legwork to get to them; from a trail of breadcrumbs (recommendations etc).

 

When I was cutting my teeth I used to look up to these folk, but now I challenge and push back (on my clients behalf’s) and it almost always bears fruit. 

[saveasteading]

30 minutes ago, Nickfromwales said:

now I challenge and push back

The great ones welcome the feedback and respect the complementary skills and knowledge of other professionals.

 

 

[Conor]

You'll need continuous ventilation for the pitch roof at a minimum.

[nealblath]

thanks for all the replies

yeah, I wondered about the continuous ventilation with the pitched roof and the flat roof both being warm roofs.

The architect said not to worry too much about ventilation though the ridge with the pitched roof having a breathable membrane under the tiles.

I'd want to fit a dry ridge system for the ventilation but if I take the EPDM over the ridge overlapping the breathable membrane on the pitched roof, will this cut off the ventilation from the eaves to the ridge?

[Redbeard]

On 08/11/2025 at 10:27, nealblath said:

We had plans drawn up by an architect and he designed the dormer roof to be a warm roof and the remaining pitched roof to be a warm roof too.

 

But what you have drawn seems, although at rafter level, to be a cold roof, or it would not, surely, need the ventilation to which you refer. A Warm Roof has all the insulation above the timbers, surely, or a 'hybrid Warm Roof' has some between and some on top of the timbers.

 

 

Edited Sunday at 20:23 by Redbeard

[nealblath]

Not sure then Redbeard tbh

The Insulation is between the rafters but we’ve to install a VCL under the rafters and then be covered over with insulated plasterboard. Then a breatheable membrane on top of rafters, counterbattens and battens, then tiles.

we’ve to join the VCL of the pitched roof to the VCL of the warm flat roof to for a sealed complete roof