Building regs and insulation loft conversion

[Freerider]

Im in the planning stage of a loft conversion.
I cant seem to find the requirements for insulating the party wall.
I contacted local building control and they said check part L and ask the insulation supplier.
Not very helpful at planning stage!
Im after a real life recommendation.
What is the normal course of action for insulating?
50s built bungalow with cavity walls.

i want the added insulation on the party wall to be the thinest possible to meet regs. Probably mineral wall to help with sound insulation.

Whilst we are at it....
PIR between rafters and over laid, total thickness?
PIR in partition walls, thickness?
Mineral wall between floor joists thickness?

Thanks in advance

 

[DevilDamo]

The advice you were given is correct though

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/697629/L1B_secure-1.pdf

Your ‘new’ thermal elements will need to meet the u-values as stated in Table 2 (Page 16) and your ‘retained’ thermal elements will need to meet the u-values as stated in Table 3 (Page 18).

There are so many different ways to meet those u-values hence why it’s up to the homeowner and/or designer to decide what and how they’d like to do it. Are you the home owner or designer?

 

[Freerider]

I am the homeowner at planning stage.
So the party wall will need to achieve a U-value of 0.30?

I was hoping someone could give me the typical insulation thickness used to achieve the current regulated U-Values.

Mineral wool against the party wall and between the floor joists.
PIR everywhere else.

im just trying to gauge the feasibility of this project in terms of lost space to insulation.

Assuming standard 12.5mm plasterboard applied everywhere.
18mm chipboard floor covering.

How thick should each insulation element be?

Party wall using standard rockwall?
Between floor joists using standard rockwall?
Between and over rafters using PIR?
Internal Loft stud wall using PIR?

thanks

 

[frutbunn]

If there already is a habitable space on the other side of the party wall then no thermal insulation is required, otherwise as previous comment. I can't speak for other BCO's but I and my colleagues have accepted a lower thermal insulation standard to the party wall if this has created problems with staircases, there is some flexibility within the approved doc, please note though you may have to increase the level of insulation elsewhere as a trade off.

There are so many different ways to meet those u-values hence why it’s up to the homeowner and/or designer to decide what and how they’d like to do it. Are you the home owner or designer?

"Designer"!!!!!! The reality is that at least 50% of this type of work is now on Building Notices, usually received the same day as the first inspection is requested even though they've been on site for a week. The builder is "sorting" it out or the plan drawer doesn't do B regs anymore, the remaining jobs are drawn by a high proportion of idiots and even some of the ones who have the skills and knowledge can't be arsed to even go in the roof space, and I'm talking about an RIBA architect here who incorrectly copied my drawing from a property next door, the ridge was offset with different pitches front to back, his redesigned stairs wouldn't fit as he assumed the ridge was central!!!! My plan was correct incidentally. Luckily my mate was doing the work and we'd both done the work on the neighbouring property a year earlier so we spotted the mistake before the job commenced.
Anyhow I digress, my point, the reality is builders/owners are becoming more reliant on B Control to sort this out on site, designers, competent or otherwise are few and far between and are getting fewer.

 

[^woody^]

im just trying to gauge the feasibility of this project in terms of lost space to insulation.

It's feasible regardless. The published thermal requirements for conversions are not prescriptive, as it's a conversion with limitations, not new build with a free reign.

The info you require regarding insulation is here in the forum or on the manufacturer's websites. Foil backed board will take up half the depth of quilt.

 

[tony1851]

Life was simpler in the old days when the regs told us what insulation to install.........