Suspended Floor insulation

[paulkillington]

Hi All
(sorry for the repost but i think i had it in the wrong area to start, its been a long week......)

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

 

[DAZB]

That is pretty much the way i would do it and always better to add another airbrick or 2 at the front and you could do the 9 X 3 inch versions to help with cross flow of ventilation. On a seperate note it is a good opportunity to assess the electrics and if you need any extra sockets etc it is easy enough to pop a few up if your circuits allow.

 

[paulkillington]

Think id be clear of any damp issues this way then ..?

 

[aveatry]

Fix roofing Battens against Floor Joists to support and retain Celotex.

Not sure what the experts think but I am sure that just some 4 inch round nails will do the job instead of roof battens.

 

[cdbe]

Foam it in. If your boards are T&G they're like to be splintered scrap when you pull them up so budget for possible replacement.

 

[paulkillington]

Foam it in. If your boards are T&G they're like to be splintered scrap when you pull them up so budget for possible replacement.

Fortunately boards are original square edge and i have a few spare originals in the loft too..
Might even nip the nail holes off the ends to get a clean hole to fix through extra work yes but no-one likes squeaky floorboards !!

 

[Ivor Windybottom]

How deep is the void? Often timber floors are just replaced with concrete as it's worry-free, damp-proof if done properly and much better insulated as you don't need to have outside air blowing a few inches underneath it to stop it rotting.

Basically you'd be upgrading to modern standards. More work and expense but with a much better end result. DIY-able too, if you fancy a challenge. Compacted hardcore > sand > damp-proof membrane (lapped up walls) > insulation slab > concrete > screed > floor covering

 

[paulkillington]

How deep is the void? Often timber floors are just replaced with concrete as it's worry-free, damp-proof if done properly and much better insulated as you don't need to have outside air blowing a few inches underneath it to stop it rotting.

Basically you'd be upgrading to modern standards. More work and expense but with a much better end result. DIY-able too, if you fancy a challenge. Compacted hardcore > sand > damp-proof membrane (lapped up walls) > insulation slab > concrete > screed > floor covering

Ha unfortunately i wont know this until ive lifted a board....

 

[aveatry]

I did mine from underneath as we had already sanded and varnished the floorboards a few years earlier. I used rockwool slabs and the space underneath was about 2 foot high it was a hell of a job in that space. As the floor was already finished I did not want to go putting holes in every section as its divided by 2 walls with staggered bricks for air flow so from underneath I removed a section of the wall so I could crawl from one chamber to another.
We have since put down an engineered oak floor on duralay which is a sort of insulation on its own.

 

[Lower]

We did the celotex option to our suspended lounge floor. It's made virtually no difference to the temperature of the floor or the room.

 

[ree]

OP,
Given historic services, eg wiring under the floor, then there could somewhere be a floor trap - if not then cut one when re-laying the boards.
You will need all the through ventilation possible so add extra air bricks.
Is there any damp showing at present?
If there's damp or rotting joist tails then come back here if you want?

Its a simple skill to lift floor boards, esp square edge, without damaging them.
Gently prise and wedge each board as you lever them up.
To relay - pilot hole and use, say, "Floorboard screws TX Flat Countersunk" or similar.

 

[paulkillington]

OP,
Given historic services, eg wiring under the floor, then there could somewhere be a floor trap - if not then cut one when re-laying the boards.
You will need all the through ventilation possible so add extra air bricks.
Is there any damp showing at present?
If there's damp or rotting joist tails then come back here if you want?

Its a simple skill to lift floor boards, esp square edge, without damaging them.
Gently prise and wedge each board as you lever them up.
To relay - pilot hole and use, say, "Floorboard screws TX Flat Countersunk" or similar.

Thanx for this will add an extra x2 airbricks to be safe, no damp \ moisture at present