Thermal bridge of vertical metalwork

[AliG]

On 10/03/2023 at 23:43, MattMiller said:

Option 1

Warm roof, replace existing osb3 18mm, damproof membrane, 50mm PIR, 12mm osb3 and rubber, raises the roof 65mm out of availible 75mm. Cant raid much more due to the Velux in the roof and the slate line. Could put in rock wool below the roof im the void ..

 

Coming to this thread a bit late.

 

Basically building control will only allow warm flat roofs in Scotland. They would take a lot of persuasion to allow anything else. I can only think the extension was never put through building control. The effort at insulating the roof is a joke. But here we are.

 

You don't need OSB on top of the PIR, the EPDM is stuck directly to it. You use PIR without the foil backing for this. Considering this you could maybe get 70mm PIR in. However, the minimum requirement for a refurbishment roof in Scotland is a U-value of 0.18, which requires 120mm of PIR. I do, however, think that if you contacted building control and explained the issue they cold give you a dispensation for this as whatever you do will be a massive improvement on the current situation.

 

Basically I wonder if you are best to speak to local building control before speculating on what is necessary. If they insist you it the 0.18 target then you will need a much thicker roof.

 

One way around the height issue is to taper the PIR at the roof junction, it could be 120mm thick up to a point then taper off towards the main roof.

 

I do think that the roof will be your biggest source of heat loss and biggest possible improvement, then you can do the windows later.

 

Replacing the windows and applying insulation to the steels at the same time would be relatively simple. Are the quotes you have based on replacing the sliders with opening doors. If you made all the windows fixed it would be cheaper and provide better U-values. However, I still reckon you are looking at around 12k including VAT fitted as a best case for triple glazed units. It looks like around 14sq metres of glass.

 

 

 

 

[MattMiller]

@AliG hi and thank you for your input , are you scottish based? 

So the 30,000+ quote for windows are all fixed other than a sliding door changed for French. As a point of exit. 

 

The info on u values is great also. I've been looking at lifting the bottom row of tiles and moving the velux window up the roof to be able to get more insulation in there. 

 

Only I've had so many roofers out and not one has been able to tell me how to do it. The closest I've come is a block who suggested removing a row of tiles but he honestly from his point doesn't know the right way about doing it all. 

Certainly can replace the flat roof with a 4 layer felt system for me. 

 

Seems odd there is so infrequent I'm able to get people out that know what the answer is. They can all replace the roof to make water tight though but not solve the insulation point. 

 

If your in the business and in Scotland give me a PM...

 

I've had one Roofer come with options to pitch roof, although I'm still not too convinced he knows how to solve the insulation of the roof. Seems like it's lost knowledge or few actually know and just throw in glass wool or the like. 

 

Has anyone used open cell spray foam as Opposed to closed cell? 

 

It's like getting our biomass boiler fixed by someone reputable. I'm resulting to being trained myself to service Eta boilers... thankfully the UK distributer is willing to help and train me up.