Building regs, thermal insulation question

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A friends building regs spec requires him to put 77mm celotex pl4000 on all exterior walls. I was thinking of doing a similar conversion. The problem is our buildings are old and have very small rooms.
Shower room internal size approx. 700 wide exterior wall one side, toilet about the same again exterior wall one side. Stairway 750 wide this is original, there is no room to even widen the rooms.
question: If you put 77mm walls inside these the rooms and passage way would be unusable. How does one meet thermal regs in these areas? Even the multi-foil system amounts to about 60mm.
Has anyone come across this complication?
It does seem contradictory to try and make a old building modern.
 
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You don't say why b/regs require you to do this?

If its a refurb job (replacing more than 25% of a thermal element) , then the requirement is to "consider" upgrading insulation and so less or no insulation may be acceptable if full insulation to current standards is not feasible

I don't know where your friend got the 77mm thickness from, it could be less
 
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Hi Woody, It's not just a refurb. He is converting offices above his business into a one bedroom flat and so has to go the full thermal, acoustic, fire proof route. The plans were drawn up by a local registered architect. On the plans is the 77mm celotex pl400 required by building regs for material change of use.
Mine will probably be classed as a refurb as it's already accommodation over a shop but I was exploring all aspects in case they tell me I have to go the full thermal acoustics route when I put in permission to fireproof between the shop and flat above.
 
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If it's a material change of use, the floor would obviously have to be upgraded for sound, fire and thermal.
But why the walls? The regs state that the insulation has to be 'technically and functionally feasible'
If that thickness makes some areas almost unuseable, then that is not practical.
You could offer to add insulation elsewhere to compensate, eg in the roof.
(yes, 77mm does seem excessive in any case).
 
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Hi Tony, It's to conform to building regs L1B extract copied from the plans I mentioned earlier.

Existing 215 mm thick solid external walls to be upgraded using 77.5mm celotex PL4000 insulated plasterboard. Strip any gloss paint or vinyl wallpaper before cutting the boards to fit the floor to ceiling height of the room. Secure boards with suitable mechanical fixings . Ensure boards are tightly butted taped and jointed using approprate tape and jointing material to create the vapour control layer.
Wall construction to achieve a U-value of 0.29 W/m2k in accordance of the latest edition of the building regulations Approved document LB1.


I hear the new rules for conversions etc are now so strict that many builders are not taking them on anymore. Please let me know any views on this I find it very interesting thanks.
 
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Architects will write anything just to get the drawings passed.

That thickness (77mm) is right for 215 solid brick walls to achieve 0,28; but it still has to be REASONABLE.

AD L1b states that where such thicknesses reduce the floor area by >5%, a reduction can be accepted.

Just get someone to do the calcs for compensating insulation in the roof.
 
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Architects will write anything just to get the drawings passed, without having to think some things through.

That thickness (77mm) is right for 215 solid brick walls to achieve 0,28; but it still has to be REASONABLE.

AD L1b states that where such thicknesses reduce the floor area by >5%, a reduction can be accepted.

Just get someone to do the calcs for compensating insulation in the roof.
 
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Thanks for your help Tony
If anyone else has had to adjust building regs due to being unreasonable in their situation, again I would be very interested to hear.
 
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