Underfloor Insulation

[gareth]

I live in a 1912 Edwardian house. In the main livinging room I have removed the fitted carpets and sanded/polished the floor boards and they look great.

However, now that winter is almost here, the room is getting a bit chilly (which I did expect). To make it a bit warmer, I have thought about fitting some insulation into the space between the floor joists from underneath. The space between the floor and the ground is about 1 metre so access is not a problem.

Does this sound like a good idea and are there any pitfalls I should be aware of?

Thanks

Gareth

 

[biffvernon]

More info

 

[Geoff Flegg]

Ahh, but to do as per the diagram involves taking up all the floorboards to get the breather membranes in - and it looks as if Gareth, like me, would rather not do that.

In my case there are a couple of loose boards at one end of the room that you can remove to get access - and with about 4' of clearance underneath even a less than small & slender individual such as myself can crawl around with ease.

Any suggestions as to if you can insulate from underneath, i.e. without taking the floorboards up? I sent a mail to the Thermafleece people some time ago but they haven't replied - admittedly I also haven't followed this up with a phone call.

I'd rather use thermafleece not just because it's greener but also because it's so much less evil to handle than fibreglass, but am prepared to use fibreglass or other products if need be.

Geoff

 

[Gervase]

You could try one of the loose fills, like Warmcel (made from recycled newsprint) which is blown into voids to provide insulation. You may have problems with electrics, however, so it would be best to talk it over with them.

 

[Geoff Flegg]

I think you might have misunderstood me Gervase - the gap under the floorboards is about 4 feet deep, therefore getting access to push slabs of insulation in from underneath is no problem - the problem is (with Thermafleece anyway) the requirement to have a breather membrane above & below the insulation, which would mean taking all the floorboards up.

I'm not quite sure what that membrane is actually supposed to do. I could staple one underneath the joists no problem - in fact you'd need to have something there to stop the insulation dropping out.

Geoff

 

[biffvernon]

So you can get down and crawl under the floor to put the Thermafleece into place? No, I can't see that you need the top layer of breather membrane and the bottom one is just stapled on to the underside of the joist as an anti-gravity device as you suggest.

 

[Geoff Flegg]

Any idea who makes / sells suitable breathable membrane?
Our roof is being replaced at the moment, and we're using a breathable roofing underlay that I guess I could use, but it's expensive and probably completely over-specified for what you need underneath a floor where it's nice and dry.

Geoff

 

[tony]

why dont you install rockwool slabs, either the type designed to squeeze in between 2 joists or just the standard type and cut 10mm wider than distance between joists and shove up.

Ive decided on the last method as its the cheapest and still gives good results, ive decided on 100mm thick.

regards

tony

 

[Mark]

I dont see why you couldnt use battens or even some sort of mesh netting stapled in place. Ive not used thermofleece yet but it looks as if it supports its own weight so shouldnt sag if you just use battens. rockwool stuff might need more frequent battens or net.

unless thermofleece is more attractive to rodents - in which case a better barrier might be wanted.

 

[tony]

Mark,

Rockwool slabs wont need any additional support if installed corectly.

ensure a tight fit between joists and it wont sag or require battens.

regards

tony

 

[Gervase]

Most batts will stay put if you knock in some two-inch pin nails into the sides of the channel every yard or so, leaving most of the pin sticking out. Assuming, that is, that your Edwardian joist spacing matches the width of the insulation batts you're after to within an inch or so!

 

[Cardiffbloke]

Hi there! I have just completed the very same job in my 1908 Cardiff Edwardian semi. I lifted the boards (had to anyway because the complete floor was shot and renewed all joists etc etc) and stapled galvanised wire net of the garden variety underneath the joists to act as a membrane. It is very sturdy, completely air permeable and wont rust. When all joists were 'underslung' so to speak i placed rolls of ordinary 200mm fibre glass loft insulation between the joists. You will find that your underfloor joists will be 15 in apart exactly the same as the loft. Then i replaced the boards tightly together to prevent the fibreclass 'travelling' up through the gaps in the boards..... MAKE SURE your underfloor ventilation system, IE air bricks are functioning properly and that you have a veritable breeze blowing under the floor. When that is done refit and seal off your skirting.... Job Done!!
Now all i have to do is sort the 'Baltic' sash windows out and i predict that next winter i will be watching Wales win the Grand Slam in my underpants!

 

[biffvernon]

Now all i have to do is sort the 'Baltic' sash windows out and i predict that next winter i will be watching Wales win the Grand Slam in my underpants!

No, no. You've missed the point. We should be insulating to reduce energy use not to increase temperature. Next year you will be able to turn the heating down, but don't discard the woolies.

 

[Penners]

next winter i will be watching Wales win the Grand Slam in my underpants

Whether Wales wear your underpants or not, they still won't win the Grand Slam.

 

[middi]

The cheapest way for insulation support is to buy a bag of three inch galvanised nail, nail them on the lowest part of the joist face and leave enough exposed to create a hook with a pair of players.

Go to the nearest fishing tackle shop a buy a reel of 20lb fishing line, keep winding this quite tight in a " Z " pattern in the joist cavities, the more the nails the closer the line will be.

Lay your insulation on top of the line.

It will cost approx £ 12 plus the cost of the insulation.

 

[Penners]

create a hook with a pair of players.

Like Lennon and McCartney, for example? :wink: