Another roof insulation post

MAJJ

Hi,

Building an extension to our home and block work is up and rafters going on. My builder is solid but want to ensure we are doing the right thing. Via another specialist firm the existing house and extension is being wrapped in EWI 100mm graphite and new windows being done at same time. Extension will have 2 large South facing velux and is being built with 9 inch blocks on flat.

Our architect spec'd the following and i would like to check with the good folks here if any advice.

'Concrete tile to match existing on 25 x 50
treated counter battens on breathable membrane on rafters to
eng. detail. Min 225mm glass fibre insulation
with thermal conductivity of 0.044W/mK. Air
tightness membrane and 52mm insulated PIR
to u/s rafter. Eaves and ridge vent
215mm concrete block, 100mm EPS graphite
external insulation with self coloured render
finish. Internally scratch coat to block walls,
50mm battens with plasterboard and skim coat finish. '

The floor is suspended also and would appreciate any suggestions on how to insulate this.

Doing the best with the low budget I have and just trying to ensure best been done for my family.

Thanks in advance,
MAJJ

BryanF

I'd put more external insulation in and probably swap the pir to the outside of the rafters

MAJJ

Thank you Bryan.

There are two insulation materials being mentioned one is the mineral wool and PIR. PIR I assume based on odd dimensions 40mm insulation and 12 mm plaster board.
Any reason to use two different materials and not use rigid board for both for both?
The internal scratch coat on block is that an airtightness measure?

Calahonda52

Re this
'Concrete tile to match existing on 25 x 50
treated counter battens on
breathable membrane on rafters to
eng. detail. Min 225mm glass fibre insulation
with thermal conductivity of 0.044W/mK.
Air tightness membrane
and 52mm insulated PIR
to u/s rafter.

Are tile battens implied?
So this is a vaulted being construction?

whats the spec on the highlighted items

Are they from the same supplier?

With the gf under the top membrane it is not enough for it to be breathable, it also needs to be wind tight so ask for the spec, not just is it w/t.

I presume its an insulated board with 12mm PB and 40mm PIR.

Is the inner side of the PB or either face of the PIR faced with Alu foil?

MAJJ

Hi Calahonda,

thanks for taking the time to respond. Appreciate any advice you can give.

Yes this is a vaulted roof. I have seen a laydex breathable membrane in the house recently but don't have spec to hand for this or an understanding of products that will be used. I will talk to my builder to confirm.

Any advice on products to use and approach to use for insulating the ceiling and floors.

Right now blocks are up, rafters going on so now is chance to check things.

Thanks,
MAJJ

Calahonda52

Am not going to X the architect spec, well, not yet , too early, its only 15:00 hrs

Have you thought about solar gain with the two velux windows, maybe time to consider external shutters..., not internal blinds that wont do the job...

What other glazing is there on south and west
What was in the tender for insulating the floor: no point in us suggesting anything if there is no mula?

If you google
suspended floor insulation
and look at the images, plenty ideas there.
What depth are the floor joists?
Are they in yet?
what span is the floor
what is in tender for floor joists?

Metric Tensor

BryanF wrote: »

swap the pir to the outside of the rafters

Hi Bryan - what's the thinking behind this?

Is it because of the EWI or is there another reason I'm not spotting?

BryanF

Metric Tensor wrote: »

Hi Bryan - what's the thinking behind this?

Is it because of the EWI or is there another reason I'm not spotting?

I just think if you must use a 'poly' based material it's a better detail to have it continuous outside the timber and have a service cavity inside the joists/VB. having 40mm ~0.023w/k warm side of 200mm ~0.4w/k is the wrong way around the better insulator should be to the colder side.

Metric Tensor

Interesting - any idea how the dew point is affected in a case like this? I'd love to have the software for checking it in the various unusual cases that we all meet from time to time!

BryanF

Metric Tensor wrote: »

Interesting - any idea how the dew point is affected in a case like this? I'd love to have the software for checking it in the various unusual cases that we all meet from time to time!

Due point should be ok remaining outside the VB, but insulation continuity & moisture control rely heavily on the installer in either case.

MAJJ

Calahonda52 wrote: »

Re this
'Concrete tile to match existing on 25 x 50
treated counter battens on
breathable membrane on rafters to
eng. detail. Min 225mm glass fibre insulation
with thermal conductivity of 0.044W/mK.
Air tightness membrane
and 52mm insulated PIR
to u/s rafter.

Are tile battens implied?
So this is a vaulted being construction?

whats the spec on the highlighted items

Are they from the same supplier?

With the gf under the top membrane it is not enough for it to be breathable, it also needs to be wind tight so ask for the spec, not just is it w/t.

I presume its an insulated board with 12mm PB and 40mm PIR.

Is the inner side of the PB or either face of the PIR faced with Alu foil?

Hi Calahonda,

Thanks for the responses and questions. Yes this is vaulted.
The breather membrane is breathe X by laydex and is in place. The topic of insulation and airtightness have just been discussed there's a difference versus what been quoted and what there needs to be.

There's a 150mm joist so that limits the depth of mineral wool but we could add PIR I assume. Any suggested materials for insulating this and making airtight. Have agreed that new blockwork will be scratch coated.

Guess I have just asked for a spec, will give you the rest of the day Seriously, any help I get I appreciate, thanks

MAJJ

Calahonda52 wrote: »

Am not going to X the architect spec, well, not yet , too early, its only 15:00 hrs

Have you thought about solar gain with the two velux windows, maybe time to consider external shutters..., not internal blinds that wont do the job...

What other glazing is there on south and west
What was in the tender for insulating the floor: no point in us suggesting anything if there is no mula?

If you google
suspended floor insulation
and look at the images, plenty ideas there.
What depth are the floor joists?
Are they in yet?
what span is the floor
what is in tender for floor joists?

Thank again for the responses.

As with many things, no solar gain has not been considered for the South facing velux, it may have to be looked at in future and I saw the velux shutter kits that can be purchased. Thanks.

Large feature picture gable window facing East, no opening.
Double French doors facing South, with side panel with opening. All frames to have vents.

Googled suspended floor insulation as suggested and yes lots of useful images to help and info to confuse We are not taking up the floor in the rest of the house, simply putting ply down and sealing. Am not convinced of the merits of putting floor insulation into the extension as the rest of house not being done. The above is been driven by mula or lack of!

BryanF

MAJJ wrote: »

Am not convinced of the merits of putting floor insulation into the extension as the rest of house not being done. The above is been driven by mula or lack of!

It's not you who needs to be convinced!!
It's the professional who signs of your extension meets building regulations

You need floor insulation.

I'm out

Best of luck

Calahonda52

Cant find:
breathe X by laydex

Op, before I am tempted to follow Bryan out the door, I will give you one more shot at this so await your response to the questions asked, plus one more:
who is signing off compliance with regs here for you.

MAJJ

Bryan/Calahonda, I have some of the answers but clearly not all the details. Genuinely, thanks for your inputs. /thread.