Intermediate floor insulation - good idea or not?

[willcrick]

I own a victorian end of terrace and after much draught proofing, curtain buying and fire lighting the house is still freezing!

The room which is particulalry cold is the sitting room (the only room you really want to be cosy!). It has 2 external walls. It seems that a lot of the heat is escaping through the external walls but also a lot into the bedroom above (which is nice and warm!).

What are the implications of putting insulation in the intermediate flooring? I am just about to lay carpet down and thought that if i insulate now is the time (the floor boards are easy to get up). I also have some rock wool insulation spare in the loft which i could easily use (no need to buy new stuff if it is already there!). I cant really afford cavity insulation at this time (although its a longer term option).

Is it common place to have intermediate floor insulation?? Does it leas to any problems?

Any advice / suggestions?

thanks

Will

 

[MdB]

I have two floor areas that I'm thinking about insulating so I'm very interested in any comments on this as well.

The first area is modern construction and I have access to one end of the floor space void via lifted floor boards above it. I would need to come up with some way of pushing the insulation to the far end but I'm sure this won't be too difficult to achieve. I'll have to buy this insulation so was thinking that something with better structural strength than ordinary rock wall.

The second area is in between the exposed beams of the rest of the house. Currently there is just a layer of hardboard beneath the floor boards (very tasteful it looks too). We don't want to lose all of the exposed beams so was thinking of dropping the ceiling level by around 70mm and then batten / plasterboard in strips between the beams. Insulation would be added in the void created though I'm not sure if an air gap is needed or not (I assume not). Hopefully this process will improve the fire protection performance and reduce the amount of noise heard through the floor. Heat loss is less of an issue though I guess it will help here also.

Comments please.

 

[NT]

Putting insulation between floors will not give you anything like the return you'd get from putting it in the loft, or on outside walls. This is why its not normally done.

If you are going to keep your upstairs cold and heat downstairs, and decide to put insulation there, a much lower insulation value is financially justified compared to loft insulation. You could achieve this within the space by using the lowest cost insulation.

In fact if your upstairs is warm and downstairs cold, interfloor insulation will cimply make downstairs even colder.

Some PPs can have heavy draughts blowing through floor cavities. In such cases it might be worth putting a narrow strip of rockwool etc around the edge for draughtproofing.


NT

 

[willcrick]

Thanks NT - just the sort of insight i was after...

I am definitely going to do something about the draughts through the floor void - my plan was to squirt expanding foam around the edge of the floor from underneath (i tried filling the gaps from above but this didnt seem to stop the draughts). I cant think of any other way to fill the dirty and uneven awkward gaps around the edge. Although rockwool would be a greener alternative...

Does expanding foam stop draughts? Does rockwool??

Will

 

[Lime]

It depends on how upstairs is getting warm.
Heat can rise via the stairwell if doors are left open.
When heat is entering the upstairs through the groundfloor ceiling then insulation can help.
I had this problem in a small cottage many years ago. The boiler was a parkray and made the upstairs bedroom too hot because the chimney breast that ran through the room gave out too much heat. This was on top of heat coming up the stairs and through the ceiling.
However with a small amount of insulation in the floor the heat in the bedroom was reduced and every where was more comfortable.
The underfloor draughts were stopped up (I used mortar or plaster around joists in the wall) and heat retained.

That was sometime ago and I used Vermiculite insulation. This material has the benefit of being able to be poured into the difficult areas but also it is a good sound insulator and fire-stop.
However with the problems of asbestos found in a few mines in the USA you may not want to use it. There are many mines that do not have asbestos contamination at all but the market has been severely damaged by reports from the USA.

 

[NT]

I would not be in any rush to use expanding foam myself. The trouble is it sets hard THEN exands, and does so with huge force. It can do serious damage.

filler/lime mortar/plaster etc will fill gaps. So would rice pudding or porridge.... not that I'm recommending them! Rockwool or cloth rags would also resist draughts, with rockwool being fireproof and rot proof.


NT

 

[Becka]

avoid expanding foam like the plague! when I was new to this old house lark I let my dad squirt it in every hole he could find (he loves it!) and have repeatedly regretted it, especially when I took away the plasterboard with its small (expanded foam filled) hole to find a mass of the stuff behind causing me a huge pain in the ass when trying to restore the wattle and daub walls i had no idea were lurking behind there .. the stuff sticks almost ireversibly as far as I can see, clogging tools when you try to cut it away and impossible to peel or chip off..

 

[Penners]

if your upstairs is warm and downstairs cold, interfloor insulation will simply make downstairs even colder.

I think NT is assuming that the reason upstairs is warm and downstairs cold is because the heating is more effective upstairs. If this is the case, then his statement makes sense.

However, I infer that the upstairs is warm because the heat downstairs is leaking up through the ceiling to the upstairs. If this is the case, then inter-floor insulation does make sense - particularly if you already have the insulation material lying around doing nothing. The addition of rockwool in the floor cavity, and a carpet upstairs should make an appreciable difference.

However, I do agree with NT that the majority of your heat loss is probably through the walls. See how things are when you've added the insulation and the carpet - if you're still freezing your wotsits off then you'll have to think about doing something with the walls.

 

[Gervase]

It's generally well worth putting some insulation under the floor. It allows you to balance your heating more effectively (warm rooms downstairs, cooler bedrooms) and most importanly it means that you are afforded some soundproofing.
With plain wood floors, anyone upstairs will hear every whisper of a conversation downstairs, and those downstairs will hear a mouse tiptoe across the room.
You can get dual purpose accoustic insulation, which has rockwool and an accoustic membrane, but given that the hard joists would conduct a fair bit of sound, I don't theink it would perform that well.
If you're planning to plaster between the joists, just put some batts of whatever insulation takes your fancy (rockwool, hemp or sheep's wool) up there - making sure to keep it away from your wires and any light fittings. It will make a surprising difference.

 

[Gervase]

And avoid expanding foam like the plague! It's vile stuff. Rockwool is a pretty effective draught stopper provided it's laid tightly and properly. It's not the nicest material to work with, but it has the advantage of being ridiculously cheap compared to other, nicer alternatives like Thermafleece.

 

[Sal]

what about the er solid kind of insulation that people use between walls on new build. any reason why that could not go in between floors (im thinking stuff like kingspan etc)?

I'm thinking of adding insulation between floors on grounds of sound proofing..

 

[Gervase]

I'm naturally prejudiced against Kingspan and Celotrex because of the amoutn of plastic they contain, but batts of fibrous stuff are easier anyway... I've used em and they can be cut to fit far quicker than the more rigid stuff like Kingspan.

 

[Penners]

Willcrick says he already has a load of rockwool lying around spare, so I reckon he'll be using that.

 

[Sal]

my thinking... for me personally... sorry to borrow the thread.. is I happen to know my ol man has a load of some sort of solid wall insulation.. going spare.. from a factory build.. and was just wondering if it would be a good idea to use it or not.

are you against the plastic on grounds of bad environmentally manufacture.. or bad for the house?

 

[NT]

if your upstairs is warm and downstairs cold, interfloor insulation will simply make downstairs even colder.

I think NT is assuming that the reason upstairs is warm and downstairs cold is because the heating is more effective upstairs. If this is the case, then his statement makes sense.

However, I infer that the upstairs is warm because the heat downstairs is leaking up through the ceiling to the upstairs. If this is the case, then inter-floor insulation does make sense - particularly if you already have the insulation material lying around doing nothing. The addition of rockwool in the floor cavity, and a carpet upstairs should make an appreciable difference.

However, I do agree with NT that the majority of your heat loss is probably through the walls. See how things are when you've added the insulation and the carpet - if you're still freezing your wotsits off then you'll have to think about doing something with the walls.

It makes no difference why the upstairs is warmer. Basic physics tells us heat will flow from the warmer body to the cooler, not the other way round. So if upstairs is warmer, the heat flow thru the floor structure will be from upstairs to down. And its that simple, regardless of any other factor.

If you want to get any real return out of insulation, it needs to go between warm house and the cold outdoors.


NT

 

[Penners]

It makes no difference why the upstairs is warmer. Basic physics tells us heat will flow from the warmer body to the cooler, not the other way round. So if upstairs is warmer, the heat flow thru the floor structure will be from upstairs to down. And its that simple, regardless of any other factor.

If you want to get any real return out of insulation, it needs to go between warm house and the cold outdoors.

I think that's broadly what I said, isn't it? However, while your final paragraph is undoubtedly correct, in this case there is still some benefit to be had from stopping the heat in the downstairs room escaping upwards into the upstairs room. Heat flows more happily upwards than downwards.

 

[NT]

It makes no difference why the upstairs is warmer. Basic physics tells us heat will flow from the warmer body to the cooler, not the other way round. So if upstairs is warmer, the heat flow thru the floor structure will be from upstairs to down. And its that simple, regardless of any other factor.

If you want to get any real return out of insulation, it needs to go between warm house and the cold outdoors.

I think that's broadly what I said, isn't it? However, while your final paragraph is undoubtedly correct, in this case there is still some benefit to be had from stopping the heat in the downstairs room escaping upwards into the upstairs room.

The only way heat can move from a colder place to a warmer one is by using a heat pump.

Heat flows more happily upwards than downwards.

[/quote]

no Heat _always_ moves from hotter to colder.


NT

 

[Gervase]

But surely hot air is less dense than cold air, therefore it rises. If not, then the Montgolfier brothers must have had some fancy trickery in their balloons!
And from the simplest empirical observation I do know that, before the floor was sorted, I could have the radiator on full-whack in one of the upstairs bedrooms, and feel not a bit of warmth downstairs in the kitchen. Yet fire up the woodburner in the kitchen and the warmth would be felt in the upstairs bedroom.
Convection may be the cinderella of energy transfer, but it does work.

 

[GK]

The Op said upstairs is warmer than downstairs but failed to say where the source of heat, if any, is.

In this situation assuming a laboratory condition dwelling then the heat from upstairs will indeed flow downstairs.

I think there has been an assumption that the ground floor is being heated, some is flowing upstairs and it *seems* warmer than down - although again, in our lab conditions it can't really be if the heat gain is from downstairs.

To willcrick, I say, if your sitting room is heated and the room above isn't, then insulating the chamber joists will keep the heat in the sitting room. If the bedroom has a source of heat that really does make it warmer than the sitting room, then some of that heat will actually be passing down through the ceiling. Under lab conditions, of course.

Don't put semi-rigid insulation with foil covering at chamber joist position.

 

[Penners]

Heat flows more happily upwards than downwards.

no Heat _always_ moves from hotter to colder.

Yes, but heat still prefers to rise rather than fall. The two statements are not incompatible.