Converting cold roof to warm

[jayc89]

We have a small-ish 4x4 flat roof extension, as part of our wider renovation project we'll be replacing the windows, blowing in some cavity wall insulation and we also want to replace the existing (50 year old) roof, with a warm one. The Architect has also proposed parapet roof going forward.

 

The plan is to follow Green Building Store's Kirkburton Flat Roof detail - https://www.greenbuildingstore.co.uk/kirkburton-passivhaus-the-flat-roof/ - laying another inner course of blocks, hanging the joists from them, then running a couple more courses of external finishing bricks. One detail I'm not clear on is hanging the joists of a box-section wall plate. What's the benefit in doing this over hanging them in a standard way; joist hangers, Tony tray etc?

[Radian]

4 minutes ago, jayc89 said:

The Architect has also proposed parapet roof going forward.

How do you feel about this? To me a warm flat roof is already too thick (from the aesthetic POV) as it presents a big vertical wall on top of your glazing units. Kirkburton Passivhaus is two-storey so the extra height doesn't look too amiss, but on a single storey extension it always looks top-heavy to me.

[jayc89]

7 minutes ago, Radian said:

How do you feel about this? To me a warm flat roof is already too thick (from the aesthetic POV) as it presents a big vertical wall on top of your glazing units. Kirkburton Passivhaus is two-storey so the extra height doesn't look too amiss, but on a single storey extension it always looks top-heavy to me.

 

Christ, don't put doubt in my mind. Our elevations are quite forgiving so we think it looks pretty good;

 

 

The section with the downpipe is existing. Everything to the right will be a new extension. 

[Radian]

On 01/02/2023 at 21:56, jayc89 said:

Christ, don't put doubt in my mind.

Why should you be the only one here not burdened by doubt?🤣 ...Just forget I ever mentioned it!

That picture doesn't give a particularly clear overview of the design overall but I'd say there's promise. What's it like in plan?

[jayc89]

9 hours ago, Radian said:

Why should you be the only one here not burdened by doubt?🤣 ...Just forget I ever mentioned it!

That picture doesn't give a particularly clear overview of the design overall but I'd say there's promise. What's it like in plan?

 

It's the dining area shown here. Also including a cross section as this area is masked on the elevation.

[Radian]

OK, in context, that actually looks pretty good to me. This is all very subjective of course. But I think you know what I was referring to with flat warm roofs. Your design is strongly influenced by set of cubic modules so the higher elevations lend to this goal. All this talk of aesthetics isn't helping your original question about construction method though!

[Dave Jones]

On 01/02/2023 at 21:37, jayc89 said:

We have a small-ish 4x4 flat roof extension, as part of our wider renovation project we'll be replacing the windows, blowing in some cavity wall insulation and we also want to replace the existing (50 year old) roof, with a warm one. The Architect has also proposed parapet roof going forward.

 

The plan is to follow Green Building Store's Kirkburton Flat Roof detail - https://www.greenbuildingstore.co.uk/kirkburton-passivhaus-the-flat-roof/ - laying another inner course of blocks, hanging the joists from them, then running a couple more courses of external finishing bricks. One detail I'm not clear on is hanging the joists of a box-section wall plate. What's the benefit in doing this over hanging them in a standard way; joist hangers, Tony tray etc?

 

stopped reading when it said "taped osb is a vapour barrier" they are obviously clueless. 

 

You need a REAL vapour barrier on the warm side of the roof brought down and sealed onto the internal brickwork the roof sits on.

 

NHBC advice offers a few options, by far the easiest to work with is Alutrix.

 

https://nhbc-standards.co.uk/7-roofs/7-1-flat-roofs-and-balconies/7-1-10-thermal-insulation-and-vapour-control/

 

 

[jayc89]

10 minutes ago, Dave Jones said:

 

stopped reading when it said "taped osb is a vapour barrier" they are obviously clueless. 

 

You need a REAL vapour barrier on the warm side of the roof brought down and sealed onto the internal brickwork the roof sits on.

 

NHBC advice offers a few options, by far the easiest to work with is Alutrix.

 

https://nhbc-standards.co.uk/7-roofs/7-1-flat-roofs-and-balconies/7-1-10-thermal-insulation-and-vapour-control/

 

 

 

I thought doing so was reasonably common, seen it mentioned on quite a few posts here and other forums. 

[Tom]

49 minutes ago, jayc89 said:

 

I thought doing so was reasonably common, seen it mentioned on quite a few posts here and other forums. 

Are you not thinking of taped foil-backed insulation boards?

[Dave Jones]

12 minutes ago, Tom said:

Are you not thinking of taped foil-backed insulation boards?

just to be clear still not an approved method.