I'm sorry... another suspended floor insulation question!

Hi folks.

I've got an 1840s Georgian terraced house. The living room is blinking cold this time of year! I guess it's caused by draught, so I'm looking to insulate under the suspended floor boards.

There are millions of posts on this and I've looked through a good chunk, receiving different, conflicting information. Also, my situation is a tad different so any help would be appreciated.

The living room is above a well-sized cellar with plenty of headroom, so working under the floor boards will not be a problem.

I planned to use a mineral glass wool and chicken wire to hold it up.

Firstly - air bricks, or lack of, maybe. I can't see any dotted around, however, we have a big coal chute. Outside, on top of this, has had a row of airbricks built up around it, with a little roof put on top. Is this my ventilation and will that be adequate? The walls never feel damp down there, floor can look a tad damp sometimes (usually after rain) but fully suspect the bricks are placed straight on to ground so this is naturally coming up through the floor, and moving through the house.

The ceiling, as you can see in the photo, is lath and plaster. Will this cause any issues or good to stay?

I've read plenty about vapour barriers. Some say above the joists, under the flooring. Some say below the joists. In the end I'm none the wiser. Some say don't bother. Is it necessary? Surely if I'm using a breathable insulation the moisture can escape anyway? Perhaps I've misunderstood. And Is the insulation meant to be put right up to the joists and floor boards?

I do also run a dehumidifier down there if that helps.

Thanks very much

The floor ventilation is to disapate any moisture, but a dehumidier will do that better, if more expensively.
Vapour barrier is more important at ceiling level than floor, as water vapour rises. However airtightness is important, as if there is bulk air movement through your insulation then it's next to useless (woolly jumper on a windy day vs windproof jacket) This will cause draughts and make the actual room cold, wheras lack of insulation will just make it cold at floor level and not cost much more in heating.
Leaving The ceiling is fine as long as there's no possibilitiy of air movement to the warm side of the insulation. The insulation has to be against your air barrier if it's not the air barrier itself. Otherwise air can blow through the insulation, across the void on the warm side, and out again. Look up plasterboard tent on google to find out more.
Other than that sounds good. Good luck.

I have recently been using this sort of fencing plastic in place of chicken wire:

http://www.wickes.co.uk/Wickes-Barrier-Fencing-Orange-1m-x-50m/p/114496

Use whatever you can get most cheaply. Polypropelene strapping is another option.

OR, since you use the cellar underneath, use something more substantial that will keep the fibres out of your spuds / homebrew / compiter / etc:

https://www.toolstation.com/shop/La...rol/sd3225/Heavy+Duty+Landscape+Fabric/p45800

Hey folks thanks so much for your quick replies. All sounds good then! Heh I didn't know the whole dot and dab thermal thing was referred plasterboard tents... made me chuckle. First thing I learned when doing this old place up! No dotting and dabbing external walls.

Endecotp how did you know I was homebrewing haha . I do have a few rolls of chicken wire to use but the landscape material looks like a great idea.

Thanks again

ritchieee said:

No dotting and dabbing external walls.

Click to expand...

You can, you just should put a parge coat on the wall first and make sure the edges are correctly sealed before adding the plasterboard. The issues are air coming from around the edges and air blowing through the inner leaf.

Moisture potentially moving from a cold space to a warm space is not an issue or concern, so no vapour barrier or similar precautions are needed.

Your issue with insulating the floor and sealing gaps is that this will most likely change the local environment by just the amount needed to allow mould to grow in the more humid conditions.

If you can't get natural ventilation in then you might need to introduce mechanical extract. Insulation of walls in itself won't help as the problem will be moist air.