Suspended Floor insulation

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28 Feb 2009
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Surrey
Country
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Hi All

Sure this has been done before but id like anyone's fresh ideas if poss.

I did drop a note to Building Control and it looks like they want the job done under building regs, which i don't have an issue with but I'm not paying them £350 just to come and look at a DIY job.

My wife and I own an old Victorian Semi-Detached cottage (not listed) and I am proposing to insulate between the floor joists in the living room as we will shortly be replacing the carpet it seems an ideal time to do it. I have a building background and am quite competent in such jobs.

The construction of the property is as follows:
Downstairs External walls are standard 9 inch cavity (not insulated)
Upstairs walls are of a solid large aggregate formed concrete type, (which is a type of construction I have never seen before.)
Downstairs dining room floor is a solid concrete.
Living room is a suspended floor with an unknown void gap (As I have not yet lifted the floorboards)
From a previous extension completed, the property was re-wired to become Part P compliant.

I have two concerns which I contacted BC to ideally get their approach on.

The Living room under-floor void currently has x2 Air Bricks in the flank wall, would air circulation in the under-floor void be sufficient once insulation has been completed or would it be best to also add one on on the front of the property.?

I am a little concerned at creating a sort of moisture trap by insulating the floor. Which would obviously be a bad thing for the potential of damp \ rot etc, please advise if my approach is incorrect and if so what would be a more compliant approach.


My proposal is to :-
Lift all floorboards in the living room.
Replace any rotting floor Joists as may be necessary.
Clean out crawl space.
Apply insulation to any water pipes
(Assuming Air Bricks are below joist level and no additional Air Bricks are required)
Fix roofing Battens against Floor Joists to support and retain Celotex.
Insert either 75mm or 100mm (or other max allowed by size of floor joists) of Celotex batts between joists, set flush to top of joists.
If air bricks are parallel with or at joist height leave 200mm gap for circulation between Celotex insert and external wall.
Using Aluminium tape seal joins between top of Floor Joists and Celotex
Replace floorboards.
Underlay and Carpet

Anyone have any thoughts ..?
Kr
P
 
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