Advice on Insulation levels in new extension

ampjohnny

Planning to add a family room extension to an existing Kitchen /Dining - i wanted to sanity check that the Insulation levels the builder has suggested are appropriate and i'm having a hard time finding what is considered optimal or good quality these days, could anyone give me a pointer or comment on the below?

Foundations and floor slab. Strip foundation with up to 4 courses of dead-work concrete blocks. 150mm concrete slab on 100mm floor insulation on radon barrier on sand blinding on minimum 150mm clean hardcore.

External walls. Concrete block cavity wall construction with 60mm cavity wall insulation. 12mm plasterboard slab to internal walls. Finished with skim coat plaster internally and a render finish externally.

Roof. Roof construction to include 175mm x 45mm rafters with breathable membrane under flat slate effect concrete tiles. Rafterlock insulation between roof timbers and 50mm insulated plasterboard slab to ceilings. Finished with skim coat plaster. 2 number Velux type windows circa 800mm x 1050mm

BryanF

No spec on floor insulation must be PIR as a minimum

Not enough in the walls should be 120mm PIR as a min.

Roof should be double battened outside joists for breathable felt to work - with eaves and ridge vents. Do not plaster slab inside. Best to plaster block to have any hope of avoiding drafts

No mention of taped and sealed vapour barrier inside rafters. That's not good detailing.

No spec on velux's - note standard velux detail does not meet part L in my opinion.

ampjohnny

BryanF wrote: »

No spec on floor insulation must be PIR as a minimum

Not enough in the walls should be 120mm PIR as a min.

Roof should be double battened outside joists for breathable felt to work - with eaves and ridge vents. Do not plaster slab inside. Best to plaster block to have any hope of avoiding drafts

No mention of taped and sealed vapour barrier inside rafters. That's not good detailing.

No spec on velux's - note standard velux detail does not meet part L in my opinion.

Thank you taking the time to provide that feedback, i could have sworn he verbally said 60mm cavity insulation and 50mm plasterboard insulation inside, would that make sense?

Assuming I confirm this is the case and that it is PIR for both the walls and floor is that sufficient?

With regard to the standard Velux detail are you referencing the glass or how it is installed?

BryanF

What is the heat loss perimeter at floor level and m2 of the extension 100mm PIR in the floor may not comply.

Walls still don't comply. If he's drylining, where is the due point? And will there be any sockets on external walls?

The velux: How it's installed, but also potientially the glazing u-value depending on the permitted variation combined areas table in part L

BryanF

Ok. That's me done. Go hire an arch or Eng to sign off on building regailtions. You'll need this if you ever plan on selling the house.

I think it's a shame that a large percentage of builders make little effort to comply with building regulations. There is an attitude that unless the client provides arch/Eng drawings , the onous is on the client to know the building regs, and the client, who is typically totally naive to this, expects the Builder to know the regulations.

Dudda

That's about the spec I'd use for a garage. It's probably warm enough to store bikes. If that's the attitude, benchmark and standard of the builder I'd keep looking. No way would I work with someone who's proposing that level. Even with an architect or engineer on board you'd have to be watching everything if that's his proposal.