Building Regs Insulation in Tiny Space

[harry_angel]

Hi, we have a section of our loft conversion which we are desperate to have signed off by the BR inspector.

 

There are a few obstacles to this however:

 

• he may insist on thicker/deeper rafters (they are currently 4 x 2s)
• even if he doesn't insist on that, he may insist on 6" Celotex insulation

 

If he insists on either of these, it renders the space quasi-unusable (it's right on the borderline right now).

 

So my question is: I think BR doesn't hinge on depth of insulation but rather quality/U rating, is that right?

 

If so is there any super insulation type product out there which won't bring the roof down further (ie. beyond the 4x2s) but nonetheless hit the required rating?

 

 

[Temp]

What span are the rafters?

 

Is the membrane under the tiles vapour permeable? If it is then you can save 50mm by not needing a ventilated void between it and the insulation.

 

Aerogel is the best insulation in the world (last I heard) but at best it's only twice as good as PIR and very expensive if you can get it. Most aerogel insulation isn't in its pure form because it's too fragile so the insulation properties aren't twice as good as PIR.

 

 

 

[Mr Punter]

Aerogel but it is crazy money

[harry_angel]

30 minutes ago, Mr Punter said:

Aerogel but it is crazy money

 

You mean $1 per cubic centimetre?! 

 

Wow.

 

At least if anyone shot at or took a flamethrower to your loft you'd be safe...

 

[harry_angel]

33 minutes ago, Temp said:

What span are the rafters?

 

Is the membrane under the tiles vapour permeable? If it is then you can save 50mm by not needing a ventilated void between it and the insulation.

 

Aerogel is the best insulation in the world (last I heard) but at best it's only twice as good as PIR and very expensive if you can get it. Most aerogel insulation isn't in its pure form because it's too fragile so the insulation properties aren't twice as good as PIR.

 

 

 

 

Thanks will check re rafters and membrane and loop back!

[PeterW]

Yep - Aerogel... sit down when you see the price list. 

 

Your alternate is use one of the multifoils but they are basically a tinfoil roasting bag, which as long as they are sealed properly will “meet” building regs. Some think they are snake oil, and  some say they work but it’s whether BC will accept. 
 

 

[SteamyTea]

Have a look at vacuum panels.

[harry_angel]

@Temp

 

Answers to your Qs: the span of the rafters is 2750mm, and the membrane under the titles is not vapour permeable...(this tiny extension bit was built in 1950)

[Temp]

16 minutes ago, harry_angel said:

the membrane under the titles is not vapour permeable

 

That's unfortunate.  Means the bco may want a 50mm deep ventilated void between membrane and insulation to avoid interstitial condensation.

 

 

 

[harry_angel]

1 hour ago, Temp said:

 

That's unfortunate.  Means the bco may want a 50mm deep ventilated void between membrane and insulation to avoid interstitial condensation.

 

 

 

 

In the words of Unlucky Alf from The Fast Show: "bugger".