Underfloor Insulation

johnpearce

Hi all
I too am wondering whether I can insulate my suspended timber floors.
I've got a 1970s detached house: the lower storey floors are tongued and grooved chipboard on joists, with a void below that varies from about 200mm to a metre. The void is ventilated by airbricks, and I'm sure the flooring is a significant element of heat loss in the house. The cavity walls are insulated by the way, and we have double glazing.
I know that the chipboard is cheap stuff, and think I would have to replace it all if it came up. So ideally I am after an insulating layer to put on top of my existing chipboard floors without disturbing them.
I know that you can get thin aluminium foil insulating rolls eg Thermawrap.
Am I likely to get any benefit by laying stuff such as this on top of the floor, and then putting the carpet and underlay down on top of it?. And might this be a bad idea for some reason?

27col

Any soft insulation that you put under the carpet will be squashed flat by foot traffic and rendered almost useless.
Incidently, if these reflective and thin insulators were any good, why is it that almost all insulation that is fitted, is hundreds of mm thick.

diana3564

I am about to start renovating a Victorian house which will involve lifting the floor boards to install central heating pipes, etc. I am very keen on insulation especially with rising prices. My question is, is what should be laid first insulation, then pipes or other way around?

Cheers

baldelectrician

I put kingspan under the floor of my existing part of the house (I had it under the new bit as it was required for building regs)

It has saved me a fortune- I didn't need to upgrade my old boiler as it copes with a 2 storey extension as well as the original house. My gas has stayed the same - depsite adding 60% floor area onto the house

I used kingspan rather than glass wool as it has better u values and I had some spare from the extension

the kingspan was £35 per sheet 8' x 4' but it has paid for itself

I put it in from below- cut it to size popped it in and screwed wooden battens in to hold it in place

brifaethebroath

I recently rennovated a 1960's built house where the void below the floor averaged around 1000mm, which i insulated from below with 100mm insulation to suit floor joist thickness. To support this i ran strips of 100mm DPC stapled into underside of floor joists and it worked ok. I have also put an extension onto the building, external kit walls fully insulated with Kingspan rigid insulation, 300mm insulation in roof space and 200mm therma-roll insulation fitted between floor joists supported on netlon. To answer (diana3564) query, floor or any other insulation should be installed post service installations as it just obstructs tradesman carrying out there works. As you may imagine new build much hotter than original part of the house even though the loft insulation is the same thickness, i've fitted 50mm kingspan and oversheeted all external room walls with plasterboard. Original build, traditional 100mm brick and dry render externally, 50mm cavity with injected foam insulation, 100mm brick and plaster internally (cold build). So i can only assume there is still a lot of heat loss through the floor. I discussed this with a friend of mine who is an Architect and he has advised me too,

• Fit Kingspan or Eco-therm below floor joists, secured with Fischer retaining plugs screwed into underside of joists.
• Divert any air from entering the void between joists where i currently have 100mm insulation to eliminate chances of condensation ocurring. Periscope vents fitted to back of base course air bricks.
• Tape up all joints in boarding, and foam up around any service penetrations etc.

I hope this helps?

baldelectrician, what thickness of insulation did you fit 100mm?

baldelectrician

brifaethebroath wrote: »

baldelectrician, what thickness of insulation did you fit 100mm?

I fitted 100mm kigspan board (not actual kingspan brand, but similar)

Pressed it against the joist from below and held it in place with 2"x1" battens screwed to joist from below

Size66

I have a void of about foot under my back room floor, that void is open to outside ambient air via 4 air bricks ( 1907 house ) the back room is FREEZING, to the point when walking in stocking feet the carpet FEELs damp bacause its so cold. Other than this problem there are no significant draughts in the room. The rooms are 11 feet hight with 20m sq of floor area - im getting a multifuel burner in there but really need some kind of floor insulation ...ideas?????;)

new_owner

Please remember that your floor needs to breath.

I used hemp to insulate mine which does cost more but is nice to handle (important if your in a crawl space) and it will allow the wood floor to breath.

Vapor barrier insulations can force moisture through the joists. You only want to do this job once.

The recommended materials for older houses are hemp, sheep wool and fibre board. No vapor barrier is needed

All the above materials can be supported with battons so if working from underneath makes the job easier.

Martyn_H

If I were to use Knauf Space Blanket Loft Insulation for ease of installation as per post #7, what thickness would I need to conform to heat loss standards?

Martyn_H

Any thoughts plse:

http://www.space-insulation.com/blanket.html

I don't understand how the R-value or the Thermal Conductivity translates into the thickness needed.