I'm going to have the house extended and as I'm doing the complete heating system I thought I'd insulate the floor. I've had a look around and there seems to be lots of expensive ways of doing it. I also found a few sites where people have suggested that a good and cheap way is to use this


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type of fencing stapled to the bottom of the floor joists which hold up spaceblanket
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so it looks a bit like this



floor_ins


comments welcome. Its this a good method thats ok for condensation?

Pete

Cunning idea... just an uneducated thought... dont you need some air flow between the joists to prevent condensation forming and thus rotting the woodwork?

It all depends how thick your insulation can be.... Rockwool type products are all well and good but you need quite a thickness compared to the foil covered foam type insulation....

Thats why the bottoms of the joists are not covered as the fencing mesh is open allowin the wood to breath. That is my main concern which is why I'm asking the question. I just know that the house is very cold in the winter and the heating can't keep up and neither can my bank account

I guess the 150 or the 200mm os space blanket which is rockwool in foil.

The name of the mesh you are looking for is Netlon.
When building from new, it is draped over the top of the joists with the insulation dropped inside.
You can still do it the way you suggest, but it'll be a James Hunt of a job.

I think it will still be easier and cheaper than pulling up all the floor and using cellotex or one of the other brands of board products.

Depending on your joist depth just go for 100mm fibreglass supported by the net.
That is used on lots of new builds and cuts out a lot of noise too,or if you are lifting the floor boards drop it in, don't cover any down lights below and watch for cables.

thanks guys looks like I'm going to be busy.

Fasten some battens to the side of your joist and drop rigid insulation in sections to ledge on them or put some slats on them and use rockwool.

Over here were it gets a little cold we put batts under the floor between the joists then close it all in with 1 1/2"or 2" hard styrofoam panels.
Mice and other small rodents like to build nests in unprotected fibreglass batts.

Scottish mice must have sharper teeth (or less brains) - the little darlings chew up styrofoam to make nests here!

Check building regs, they are very specific on insulation

Why use Rockwool, new glassfibre has the same u-values slightly under for sound performance but is cheaper and easy to work with.

My neighbour did this , it worked really well. He used even cheaper garden netting used for sweet peas & strawberrys etc.

tri iso. all day.

best by far.

Most Building regulations officers don't usually accept Tri Iso.

Insulation and type now has to be calculated by an approved energy assessor using software called SAP unfortunately gone are the days where you just put in a bit of rockwool, covered by part L energy efficiency in buildings.

So if you have to go for building regs approval, best to get their input first or you may be waisting your time.

Another thing to consider is the amount of glazing you have in the new extension if its more than 25% you open up another can of worms.

Most heat goes out the walls, windows & roof. Better returns investment there.
Thick carpet on floor to stop draughts,t hat's all.

tri iso and building regs.

Because of the high U values it shoudl pass with private inspectors. the council ones generally have different requirements outside of building regs.

i past using tri iso in the roof of my large loft conversion. all i used was tri iso on roof and kingspan 50mm in the space between the boards and the 25mm gap to the roof.

and in the floors and in the walls.

had no issues at all and its always warm in the winter with no heating in the loft at all.

its 7.6m x 6.2 m loft convertion and full tri iso all way round. solar glass helps keep it warm but its always ok without any heating.

quote:

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Originally posted by big-vee-twin
Most Building regulations officers don't usually accept Tri Iso.

Insulation and type now has to be calculated by an approved energy assessor using software called SAP unfortunately gone are the days where you just put in a bit of rockwool, covered by part L energy efficiency in buildings.

So if you have to go for building regs approval, best to get their input first or you may be waisting your time.

Another thing to consider is the amount of glazing you have in the new extension if its more than 25% you open up another can of worms.

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Building regs specified 100mm of Kingspan (or celetex) in my loft extension. In the roof and in the walls.

They also specified 150mm of rockwool between the 9" ceiling joists.

It looks an expensive outlay but upstairs now we hardly need to put the heating on. All the rad thermo's are on No1. Well worth the initial outlay IMO.

This coming winter I plan to have a log burner in that will reduce the need for the central heating even further!

LG,
Steve

There is no doubt Tri Iso is good but unfotunately the testing methods used by the manufacturer doesnt strictly comply with the BS which is why a lot of Building Control guys private and Council do not accept it, it has to be said the building regs it allows the discretion of the individual officer to decide.

Thats why you need to consult the building control and then maybe hire an accredited energy assessor like me.

Not sure from your OP, but are you talking about the ground floor floor or the first floor floor here?

When we extended (single storey) and added a conservatory the building regs/inspector specified the Kingspan type board in the ground floor floor and walls and rockwool in the ceiling.

I went to town elsewhere and upped the rock wool loft insulation from 100 to 250mm. This made a big difference last winter to the heating demands. It hasn't helped to keep the place any cooler in the recent warm weather though.

If it wasn't such as PITA I'd really like to add some insulation between the ground and first floor as well to cut the sound down.