Under floor insulation for joist and floorboard floor with crawl space?

[rcx132]

I have a 1930's house, fairly typical I think, the ground floor is made of joists with floor boards and has had an oak floor added on top of that. The crawl space is vented. During winter the floor feels very cold and I've been wondering about retro fitting insultation from underneath, ie to go into the crawl space and put insulation between the joists.

There is a small trap door to get into the crawl space. It can't be enlarged because of the oak floor, so getting kingspan through it may be difficult. Mineral wool would be easier.

Does anyone know what the building regs say about this type of insulation? I've asked builders and some have said there's nothing to it, just put in the insulation, others have said that the oak floor and boards need to be removed (destroyed), so that a membrane can be put on the joists.

The council used to give advice on building regs, but they've now stopped doing this

 

[mike os]

Both are fine … and anything is better than nothing.

No need to membrane as long as there’s an air gap

 

[James1979]

I know nothing other than I had the same problem.

I just put rockwool slabs between the joists. I’m not that bothered about regs. It’s fireproof and it saves me money.

Unless you’re looking to sell it I wouldn’t worry. Do whatever is best for your pocket in the time you’re likely to live there.

 

[Pigeon_Droppings2]

I've done the same....one property I used kingspan (that was a floors up renovation)....the other I'm using rock wool slabs from underneath....it made a massive difference to my 1930s house in London....it also has an oak floor over the top of the floorboards like yours.

I found it easier to measure the joists and roughly cut the slabs above ground and then fit them. You'll need a way of making sure that the rock wool doesn't fall down!.....also wear a mask for sure.

Pay close attention to the edges of the rooms....I've also been using the new polyester insulation too...nicer to handle but not as fire resistant as rock wool.

My London house was done 10+ years ago....not had any problems.

 

[gaz1]

depending on your beams try to use 8" insulation

 

[dobbslc]

It would be worth checking the joist center's before ordering loads of slabs as you might find they are all over the place! Sounds like a nasty job

 

[gaz1]

on another note here id consider running 2 lengths of pex piping as underfloor heating per joist but thats up to you

as this will heat under the wood warming the floor you dont want it as a heat store but as a warmed floor

then if you so decide you can add another layer of insulation under the whole floor

 

[vw1]

I didn't have the luxury of getting underneath my floor boards in the hall so I took mine up . I used 50mm pir I think can't remember thickness but definitely no less than 50mm. I foiled taped all the joints etc.

Who can spot Henry?

 

[voipio]

Where's Wally?? ;-)

 

[Gareth J]

If you take up the floor, advantage is that you'll be able to fit a draught proofing membrane below boards and trap behind skirtings.

From below, nets or breathable membrane (membrane has advantage of helping draught proofing) stapled to beams. It's possible to build a sort of membrane hammock so you can get more than the joist depth of insulation and help stop cold bridging through the joists.

Another school of thought is to fill the entire void with EPS beads. Feels risky. But proponents have assured themselves risk of joist condensation and rot is reduced.

 

[brightspark]

staple this to the underside of the joists https://www.screwfix.com/p/ybs-airt...2m/6520p#product_additional_details_container

 

[Gareth J]

staple this to the underside of the joists https://www.screwfix.com/p/ybs-airt...2m/6520p#product_additional_details_container

I *think* consensus is that, unless you put a vapour proof membrane on the warm side, you should keep it vapour open on the cool side. Because, as the bottom of the (now insulated) joists will be significantly cooler, there's a risk of condensation and damp on bottom of joists if you have something that won't let vapour out. Plus, that stuff is quite pricey as insulation goes.

 

[addjunkie]

My advice would be get someone else todo it for you. I once did over head fibreglass insulation under an over garage extension. Twas an awful job!

 

[brightspark]

My advice would be get someone else todo it for you. I once did over head fibreglass insulation under an over garage extension. Twas an awful job!

not if u wear throwaway white ovealls goggles gloves and a mask on a cool day

 

[fractured]

My advice would be get someone else todo it for you. I once did over head fibreglass insulation under an over garage extension. Twas an awful job!

Don't use fibre glass, it really is awful stuff. You will be scratching for days and you really don't want to breathe it in.

Rockwool (mineral fibre) is not as bad. You still don't want it on your skin, it will still make you itch, but not as bad as fibreglass.

Which ever you use, use a good mask - remember if you are under the boards you are in a confined space.

I can't tell you how to insulate your house, but I used to make industrial ovens and the panels were packed with rockwool slabs which we cut with standard wood saws. This will create lots of dust so do it outside if possible as you don't want it inside your house.

I am watching this with interest as I am in a similar situation be it in an early 70s house.

 

[gaz1]

since i have mentioned this i will link to a video for you

remember its low heat for the wood its not to used as a heated slab floor as its not good for the wood floor at a high heat output

 

[Pigeon_Droppings2]

The new polyester insulation is nice to handle...don't even need gloves. But it's more expensive...and less fire proof.

I think rockwool is ok to use...main injuries I had was knocking into stuff.

One thing I did was clean up under the floor before I started....then put down a couple layers of cardboard to lay ( there was limited room).

 

[armalites]

When I did my roof I used sheeps wool insulation because it's breathable, has other properties and is eco friendly but it is joy to be able to work with insulation that doesn't make you itch, you don't need a mask and you don't end up with bits everywhere.

 

[Am333rcr]

depending on your beams try to use 8" insulation

we have just done that or i have .

it has made a big differncs still an air gap there. its recycled plastic stuff so no jaggie fIbre glass

 

[Misterg]

My advice would be get someone else to do it for you.

+1

I did under our lounge floor with Rockwool. The 'deep end' of the crawl space wasn't too bad - there's enough height to crouch down. At the 'shallow end' you're lying on your back, wiggling around on your shoulder blades with your nose touching the joists.

Absolutely hatefull job.