Best solution to insulate suspended floorboards

cargen

Hi,

Any recommendation on insulation of suspended floorboards for a 3 bed semi detached. The area is c55 sqm.

I am looking for a good solution without breaking the bank.
Could I avail of the seai grants?

Thanks

BryanF

http://www.boards.ie/vbulletin/showpost.php?p=76683844&postcount=8

smjm

This set of 3 videos might be of interest to you: https://www.youtube.com/playlist?list=PLH911xvwsOXaPhEfY6O3TwokpKK6O97YX

The comments are worth a read too.

cargen

Thanks for the links, very helpful.

Any idea of the costs in Dublin area for this type of work. Could I avail of seai grants.

smjm

cargen wrote: »

Thanks for the links, very helpful.

Any idea of the costs in Dublin area for this type of work. Could I avail of seai grants.

No idea on costs I'm afraid.

It doesn't look like you could get a grant either: http://www.seai.ie/Grants/Better_energy_homes/Better_Energy_FAQ/Homeowner%20FAQ/What-type-of-work-can-I-get-a-grant-for-.html

Calahonda52

have a look here for technique:
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx

Cost is very difficult to give as you give no ideas as to the existing flooring type and the number of rooms etc.

In passing, this job is quite difficult to get done RIGHT. the main problem is getting the airtightness right to stop the air passing THROUGH the new insulation

cargen

Calahonda52 wrote: »

have a look here for technique:
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx

Cost is very difficult to give as you give no ideas as to the existing flooring type and the number of rooms etc.

In passing, this job is quite difficult to get done RIGHT. the main problem is getting the airtightness right to stop the air passing THROUGH the new insulation

Thanks,
Floor area is c50 sqm , 3 rooms and entrance.
Floor is just made of floorboards no carpet or anything else on top.

It would be great to have a high level idea of the cost.

micar

I'm looking at doing the same thing.

Choice between using rockwool, sheeps wool or polyurethane sheets(Kingspan, quinntherm etc)

Still Undecided what to use and which would be easier to install.

You need to look at all, determine the u value required and cost of each method to achieve this.

Need to use air tightness membrane between insulation and floorboards.

Depending on insulation, you'll need to use netting or clips or nails to hold the insulation in place.

The membrane will need to be taped to the sides of the wall behind the skirting board.

You cannot block the vents.

James 007

It will depend on how the work can be done. Do the floor boards need to come up or is it possible to gain access under the floor by just removing some floor boards and working from underneath. I have done this before, it is a messy job especially if using fibreglass insulation and not easy if access is restricted. Essentially a person lying on ones back under a floor with an access space height of less than 0.5m.

If the floor boards need to come up can they be taken up without damage to them. Usually old houses the floors are fixed down using iron nail fixings. These are difficult to prise up without damage to the floorboards. Do you expect to lift all the floor boards for the works, if so all the furniture would have to be removed too from the rooms.

Calahonda52

micar wrote: »

I'm looking at doing the same thing.

Choice between using rockwool, sheeps wool or polyurethane sheets(Kingspan, quinntherm etc)

Still Undecided what to use and which would be easier to install.

You need to look at all, determine the u value required and cost of each method to achieve this.

Need to use air tightness membrane between insulation and floorboards.

Depending on insulation, you'll need to use netting or clips or nails to hold the insulation in place.

The membrane will need to be taped to the sides of the wall behind the skirting board.

You cannot block the vents.

Good stuff here Micar.
Just the one I bolded needs a bit more thought, IMO iff using non rigid insulation.

It the A/T layer is positioned as you suggest, which has been conventional practice since we moved out of the caves in Africa, then the air blowing through the space underneath with have unfettered access to blow THROUGH the insulation, thereby reducing, or even eliminating the U value.

If you think about it for a moment, and ignore the rain issue, a roof insulated in the same way always has a windproof layer on the cold side....

If this logic is correct, then the rigid insulation, as suggested by yourself above gets better performance for your buck.

I agree with James 007 re the practical issues, been that soldier, hence It brings us back to properly done rigid.

gctest50

Not be simpler ( from an airtightness POV ) to :

drop the floor ~ 100 or whatever mm,
sheet it,
seal the gaps between the sheets and wall,
put down floor insulation that can take the load,
sheet over that and then flooring ?

( obv. take care of underfloor vents, dpc, etc )


instead of staples and netting and airleaks and air bypassing your bits of solid you've cut up

BryanF

micar wrote: »

I'm looking at doing the same thing.

Choice between using rockwool, sheeps wool or polyurethane sheets(Kingspan, quinntherm etc)

Still Undecided what to use and which would be easier to install.

You need to look at all, determine the u value required and cost of each method to achieve this.

Need to use air tightness membrane between insulation and floorboards.

Depending on insulation, you'll need to use netting or clips or nails to hold the insulation in place.

The membrane will need to be taped to the sides of the wall behind the skirting board.

You cannot block the vents.

Anything but PIR (kingspan type) - the 'wools' are just easier to get into gaps etc.

I used Breathable roof membrane instead of netting

PIR can be handy underneath the floors at the rising walls to help reduce thermal bridging, a lot of foam would be required to ensure continuity.

You'll find air-tightness tape is great for membrane to membrane but flexible gun sealant is easier for existing wall to membrane junctions.

It's important the person doing this work understands the final requirements of the timber floor.

BoardsMember

gctest50 wrote: »

Not be simpler ( from an airtightness POV ) to :

drop the floor ~ 100 or whatever mm,
sheet it,
seal the gaps between the sheets and wall,
put down floor insulation that can take the load,
sheet over that and then flooring ?

( obv. take care of underfloor vents, dpc, etc )


instead of staples and netting and airleaks and air bypassing your bits of solid you've cut up

That looks to me less reliant on someone getting a nasty job done correctly, i.e. you will not necessarily discover the "missed bits" on the other approaches suggested, whereas this method looks to be easier & more reliable.

Calahonda52

BoardsMember wrote: »

That looks to me less reliant on someone getting a nasty job done correctly, i.e. you will not necessarily discover the "missed bits" on the other approaches suggested, whereas this method looks to be easier & more reliable.

Dropping the floor joists may mean having to drop the dpc inside the house lower than the dpc on the walls so that is an important detail to be considered.
The external wall vents may need to be redone, and possibly a lot of wiring and CH and other plumbing.

James 007

Calahonda52 wrote: »

Dropping the floor joists may mean having to drop the dpc inside the house lower than the dpc on the walls so that is an important detail to be considered.
The external wall vents may need to be redone, and possibly a lot of wiring and CH and other plumbing.

Sometimes external vents are just one brick high above ground level or less so this may not be possible. Also fire hearth may be supported on main timbers/joists so this may also require adjusting

Heartbreak Hank

Sorry if there is a more up to date thread on this subject than this one.


Is there a minimum void required below the insulation? In my house (1950s/1960s semi d), based on lifting a couple boards, I have ~200 mm from top of joist to ground level. The joist is 110mm, so there is 90mm below the joist. I was intending to use 100 mm PIR on battens between the joists leaving a ventilated depth of 100 mm. Is this a condensation / rot risk?