Insulation query!

[korky]

I am currently building a 3500sq ft dormer house.

Quick questions and advice on whether the spec is ok?

Walls -
6" block, air gap, 60mm kingspan insulated board, 6" block.
I am wondering whether I would get away with 38mm insulated plasterboard or will I need at least 50mm insulated plasterboard on all external walls as the cavity wall insulation is very poor? What u value would I get?

Windows -
Full u value of 1.2 (Future proof double glazed window) all air tight and tapes around fittings.
Would triple glazed option be worth the extra money?

Precast slab and 6" of screed between ground and 1st floor with suspended ceiling and 12.5" plasterboard (No insulation needed?)

Lintels -
All insulated with 60mm between steel and filled with an extra 60mm before been shuttered or filled with blocks and then covered with insulated plaster board.


Upstairs
Slooped Roof -
140mm Moy heat shield, actis super 10, tyvek supro felt/membrane counter battoned and 12.5 plaster board.
I will also run 200mm of rockwool along flat part of attic roof. Proposed u value of 0.12/.013??
Would insulated plasterboard be overkill?

Also a very topical question, is whether to leave trap doors along wall for extra storage or does this cause trouble with heat loss?

Studding
100mm moy acoustic roll between all studding

Velux
All tape and insulated around edges
window u value 1.1

Pipes
All lagged and insulated

As asked at start, is that a sufficent spec of insulation or can someone advise me of another idea?

Thanks
Korky

 

[onq]

Korky,

With the best will in the world, I have to make some serious comments on your proposed specification.
75mm loading screed is what you'd use for a 200 PC slab with a 6-7M span checked by an engineer.

Your wall specification is a non-compliant and the rest of it seems to be badly mismatched.
Your windows have a better u-value than your wall construction, and that's not right.

Please appoint both an architect and an engineer to design a dwelling of this size.
As part of this you need to have a set of technical working drawings drawn up.

Afterward you need to have a BER assessor perform a checking calculation.
Otherwise you'll just be throwing money and brochures at this project.

And if you're including a lot of services you need an M&E on board.
Without any professional input you will have no credible certs.

This will come back to haunt you when it comes to selling.
Personally I'd have a Q.S. on any building over €100K

Fail to take my advice and you'll waste money.
You need to take professional advice on this.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.

 

[korky]

Onq,
Apologies as my topic may have been misleading.
I am currently at roof level and have an engineer, architect and contractor building the house.
I was just asking about the insulation spec as to me it did not seem right. I knew cavity walls in particular were not properly insulated and that is why opinion on the size of insulated slab and possible pumping cavity was more so what I was I looking for?

As for the roof soec that was what the spec a reputable company designed for me?

 

[Superman]

Would triple glazed option be worth the extra money?

Probably. Need a preliminary BER (i.e. get someone to do a BER based on your specification and then vary it depending on putting in triple glazing).

Precast slab and 6" of screed between ground and 1st floor with suspended ceiling and 12.5" plasterboard (No insulation needed?)

Generally no need for insulation. 6" screed sounds huge - I assume the Engineer sized it?
Do you have underfloor heating upstairs? You might consider insulation in that case (to make sure the heat transmits up rather than down.
Make sure the location of insulation is ok'ed with the engineer.

I will also run 200mm of rockwool along flat part of attic roof. Proposed u value of 0.12/.013??
Would insulated plasterboard be overkill?

You need a preliminary BER to tell you.

Also a very topical question, is whether to leave trap doors along wall for extra storage or does this cause trouble with heat loss?

It might cause problems depending on how well draught proofed and insulated it was.
My preferred detail is to follow the line of the roof with the insulation. So the entire building envelope is heated. This avoids problems with having frozen bursting water tanks or draughty uninsulated trap doors.
You can put a small amount of insulation then on the ceiling so that the attic isn't "fully" heated.

As asked at start, is that a sufficent spec of insulation or can someone advise me of another idea?

Sounds pretty good. The fact that you are asking the questions and that it isn't a BER person controlling everything (from airtightness to insulation) is slightly worrying however.
That is to say, if it is you who asking the questions, is there anyone ensuring that all construction details comply with achieving the relevant airtightness requirements etc.

 

[onq]

Korky,

I've been out of town for a week and I'm only now catching up on all these threads.

In relation to your question, I think we are both agreed that the insulation specification is unusual, for example -

Why are you running both Moy 140mm and Actis Super 10 - and then using a third insulator (Rockwool) on another part of the roof?

The overall specification seems all over the place.

Superman has guided you in the right direction by suggesting your insulation should follow the line of the roof, but this is subject to the junction between the flat roof and pitched roof sections being correctly carried through and more importantly, the ventilation of the interstitial spaces and the sealing of the insulation against wind infiltration all being carried out correctly.

However, your wall construction and insulation seems haphazard.
Why are you using 150mm/6" blocks at all - is this a Quinn-Lite block?

For a house that size with comomensurate loads and spans up to 5-6M I would be using 215mm solid concrete inner leaves and internal walling to assist with taking heaving point loads and help support concrete floors.

Were timber floors to to be used I would also expect to see steel beams and columns helping to transfer the load and transmit them to ground.

If you have professionals already appointed you should be directling your queries to them, and a BER assessor or your architect should be advising you.

I prefer to see a Mechanical and Electrical Consulting Engineer appointed on a high specification house - they are more complex than developer=spec commercial buildings these days!

A good one should be able to model your houses heat loss using HVAC software suited to your Mechanical Ventilation and Heat Recover System.

Er, you ARE using and MVHR system aren't you?

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.