Cold suspended floors - will a good underlay help?

[IJWS15]

Many years ago insulated a suspended floor with my father.

Started at one edge and took 2ft of boards up, chicken wire nailed to joists and 4" of rockwool laid, most of boards re-laid with no gaps and next couple of feet lifted. And so on accross the room.

Didn't move any furniture out, just lifted it accross when we got to it.

Took 2 evenings and at the end we had to add 9" of new floorboards - the proper way to do it and made an enourmous difference.

 

[Paintguy]

You make it sound so easy

Maybe I should expand upon the reason why I don't think I can do that. Maybe some of you reading this could come up with a solution I haven't thought of.

Basically my 100mm joists are supported by several dwarf walls running the width of the house. I've seen these before but they are normally very "gappy" between the bricks leaving plenty of ventilation (sorry if there's a technical term for this kind of wall, I just don't know it). My walls are solid so the only cross ventilation I get is from the gap produced by the joist, i.e. under the floorboards and over the tops of these walls.

If I were to fill the space between the joists with insulation as you suggest (and as I'd prefer) then surely by blocking these ventilation gaps there would be no air movement under the middle of the floor (as it's boxed in by these walls) which would lead to problems.

So back to my first post - I'd either have to only fill sections of joist that don't run over these walls leading to cold spots, or maybe I could put 50mm (ish) of something like celotex tight up to the floorboards, leaving a 50mm gaps over the tops of the dwarf walls for air circulation. Or if I were to completely fill these areas with a fiberglass type of insulation (rather than rigid boards) would that allow enough air to move around?


Even reading that back myself it sounds confusing so I hope you guys can make sense of it. I can (try and) draw a picture if it helps!

Thanks,
Andy.

 

[Paintguy]

Did a quick picture anyway

As you can see, if I block the area above the walls with insulation I'm not going to get any air movement around the centre of the underfloor area. Air bricks are in the front and rear walls as pictured. Left wall is party, right wall has concrete-floored extension.

Any clever ideas appreciated

 

[lymmranger]

I give up

.....You originally said you had no intentions of insulating under the floor (which is supposedly the "proper" answer)

I suggested not only a quick fix, but one I had personally done sucsessfully in my own home.

 

[Paintguy]

I give up

.....You originally said you had no intentions of insulating under the floor (which is supposedly the "proper" answer)

I suggested not only a quick fix, but one I had personally done sucsessfully in my own home.

In my first post:

Is the above likely to make any noticeable difference? Or do you have any other ideas on doing a proper insulating job underneath, bearing in mind the dwarf wall issue?

So from the start I've been looking at both options

 

[jabuzzard]

You could always knock a few bricks out the dwarf walls to retain air movement. Alternatively you could drill a series of 25mm holes through the bricks, a SDS+ drill will make light work of it.

A "cheap" way of filling the gaps between floorboards is to make paper mache out of old newspapers. Personally I would say that covering the floor with paper is just as effective as hardboard, costs a lot less, is much easier and does not add to the floor height.

 

[Paintguy]

Thanks for your reply, although things have changed a bit today.

We've taken up the old carpets and I found an access panel in the front room floor. I can get a much better look under the floor now and there does appear to be some large gaps in the walls running down the centre of the house, enough for me to crawl from one end to the other. There are some sturdy timbers bridging these gaps with the joists resting on them.

So I'm happy that there'll be plenty of air circulation now so I just need to pluck up the courage to crawl around under the house (I'm not good in confined spaces!!)

I have loads of 100mm loft insulation spare so I might as well use that, even though I know it won't be as effective as rigid board.

As for draught proofing, I decided to go the paper route too. It used to work well enough in the old days when my mum would lay down loads of sheets of newspaper before the underlay! So I'll be taping up the joints between the boards (I use boxes and boxes of masking tape in my job), then putting a layer of thick flooring paper down, taping the joints and edges too. Some 'spandy foam and/or caulk in the gaps under the skirting boards and we ought to be pretty much draught free.

Also, having seen the type of underlay we have at the minute a decent PU is going to be a massive improvement I think. It's that waffle stuff with virtually no thermal insulation and plenty of holes for draughts to propagate.