Insulating between ground floor joists

[Trowelblazer]

I am currently in the process of renovating an Edwardian house and have been insulating all the ceilings before reboarding and plastering. I would like to insulate between the floor joists on the ground floor as well but when I have checked there is not a big enough crawl space to get under it and work.

I am thinking of taking up all the floorboards and stapling netting to the underside of the joists before putting on 100mm Rockwool, leaving a 70mm air void above the Rockwool for pipes etc.

1. Can anyone tell me if this is the right way to go about it?
2. Does anyone know what the current building regs are on this?
3. Can anyone let me know if this will cause a damp issue?

The reason I am asking is that I have had completely conflicting opinions, some people maintain that the insulator must be touching the underside of the existing floorboards and others have stated that an air gap must be left which is really confusing so any opinions on materials, installation etc would be really appreciated.

Thanks

 

[Mattatooi]

You want the insulation to be sitting at the top of the joist just below your flooring. I did this recently, and some advise.

If you do go for netting do not get cheap netting. If its cheap its too flexible and springy. I did this and it was an effin nightmare. Also being cheap, the flipping insulation would sometimes get caught on it and pull it (I did not lift my whole floor). I persevered with it because I couldn't return it, but I would def spend more money on better netting if I did it again.

However, you could consider putting in wooden battons. Its cheap and way faster than netting. You can put them every 0.5 - 1 metre. As said above, depending on your floor you may not need to lift the entire floor. I decided on this option after I started taking the floor up. I had tounge and groove and it was really well put down, and was very hard to get up. So I decided to take out 2 strips every 4 strips of tounge and groove. This meant I then fed the insulation through. I was also not too concerned with the finish when relaying it as we are putting new flooring on top.

I had some awkward joists widths that were wider than 400 mm but less than 600 so getting them to sit nice was a pain. I used wooden battons on these quite close apart, because I was so fed up with the **** netting and I knew it would be a pain, and I have to say. Using battons was waaaaay faster and waaaaaaay easier, and I would say waaay cheaper! If you cut them right, you dont even need to hammer/screw them in as you can just wedge them in.

I am a DIYer and asked a friend builder about doing it, and he said its dead easy and I could do it myself no bother. HE suggested battons, and I said I was gonna go netting. Wish I listened lol. The only slight downside of batons is, if your width is not a snug fit you can get little bit of sag between joists. But ideally you want to cut bigger width than the joists so it essentially holds itself in.

Also, dont forget to label your flooring so it goes back in same place, including orientation of it too!

 

[Trowelblazer]

Thanks for the advice, much appreciated

 

[geraldthehamster]

Consider using Celotex board as an alternative. There's a theoretical benefit in U-values, and a practical benefit in preventing draughts if you seal the edges with expanding fpoam. Also less fiddly.

Your type of job has been discussed several times here - try searching for "insulating suspended floor", for ideas.

Cheers
Richard

 

[Mattatooi]

Forgot to say, also make sure any electrical cable is below the insulation and is not covered in it. And of course do not block up any vents! Also prob a good idea to throw some pipe insulation around any copper heating pipes while you have the chance. In theory it will be colder under your floor. Its not expensive to do.

 

[Trowelblazer]

Thanks Richard,

I have had a look and there is lots of info but a lot of it conflicting info.

I.e do you put the insulator directly under the floorboards or leave an air gap, do you use a moisture membrane etc etc, the list goes on and on

Thanks anyway buddy, well appreciated

 

[geraldthehamster]

Thanks Richard,

I have had a look and there is lots of info but a lot of it conflicting info.

I.e do you put the insulator directly under the floorboards or leave an air gap, do you use a moisture membrane etc etc, the list goes on and on

Thanks anyway buddy, well appreciated

You don't need an air gap, and you don't need a vapour barrier (although foil-backed Celotex gives you one anyway).

Cheers
Richard

 

[Trowelblazer]

I have had a look and I think the battens could be a great idea. I assume you just wedge them in between the joists like noggins, will be much quicker than using netting

cheers

 

[Trowelblazer]

Thanks Richard much appreciated buddy

 

[freddiemercurystwin]

I have had a look and I think the battens could be a great idea. I assume you just wedge them in between the joists like noggins, will be much quicker than using netting

cheers

Normally they are small battens nailed to the side of the joists running parallel with them, rather than noggins, which can fall out if not mechanically fixed.

In fact you can actually just use small nails without any battens.

 

[geraldthehamster]

I have had a look and I think the battens could be a great idea. I assume you just wedge them in between the joists like noggins, will be much quicker than using netting

cheers

Normally they are small battens nailed to the side of the joists running parallel with them, rather than noggins, which can fall out if not mechanically fixed.

In fact you can actually just use small nails without any battens.

That would work for Celotex, but not for Rockwool, which I think is what the OP was suggesting using. I think the suggestion in regard to that was to wedge battens across, noggin-style.

Cheers
Richard

 

[freddiemercurystwin]

Ahh thought he was using celotex, ahh well, I would still mechanically fix though rather than rely on them being wedged.

 

[geraldthehamster]

Ahh thought he was using celotex, ahh well, I would still mechanically fix though rather than rely on them being wedged.

So would I. Then again I wouldn't use Rockwool, I'd use Celotex Have done, in fact.

Cheers
Richard

 

[Mattatooi]

Yes screw/nail them in. Whichever is easier for you. I found actually screwing was easier for the few bits I did do.

 

[geraldthehamster]

I reckon that if you drape Rockwool over battens, at 0.5-1m intervals as has been suggested, then over time the Rockwool will sag and compromise your draught proofing.

Cheers
Richard