Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I envisage nailing laths up to the joists near one end of each room,
sticking a strip/slab of fairly inflexible insulation into each gap, &
nailing more laths up & repeating as necessary to fill all the spaces
between the joists.

Does that sound right?

Is it possible (or too expensive) to get strips already in the right
width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

For the small gaps where joists are close to the side walls, should I
just stuff rockwool or something like that up in there?

Thanks.

In article ,
Adam Funk writes:
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms.

I would want to establish with some certainty that was where the heat
was being lost before putting in the effort. The floor is usually the
place least heat is lost, unless it's bare boards with gaps allowing a
draft to blow through.

Otherwise you risk putting in all the effort, and not seeing the gains
you wanted.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 08/01/15 10:48, Adam Funk wrote:
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I envisage nailing laths up to the joists near one end of each room,
sticking a strip/slab of fairly inflexible insulation into each gap, &
nailing more laths up & repeating as necessary to fill all the spaces
between the joists.

Does that sound right?

Is it possible (or too expensive) to get strips already in the right
width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

For the small gaps where joists are close to the side walls, should I
just stuff rockwool or something like that up in there?

Thanks.


Can you use PIR insulation board *under* the joists - that would save
much cutting.

However, make sure the space under this all is ventilated (rather than
the air bricks/vents opening between the joists) or you'll get damp
problems.

In article , Adam Funk
writes
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I envisage nailing laths up to the joists near one end of each room,
sticking a strip/slab of fairly inflexible insulation into each gap, &
nailing more laths up & repeating as necessary to fill all the spaces
between the joists.

Does that sound right?

All points have been asked and answered a hundred times before.

I've contributed many times on this subject sharing long experience, the
latest being easily within the last couple of months, but I'm afraid I
just can face rehashing the same old script again.

Please have a search on google groups for the pertinent discussions.
--
fred
it's a ba-na-na . . . .

On Thursday, January 8, 2015 11:00:06 AM UTC, Adam Funk wrote:

width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

Get the special saw; it is very sharp but has no teeth. If you use an ordinary saw you get annoying bits everywhere. Also, chickens (if you have them) enthusiastically eat the little bits thinking they are food and it's not good for them.

Robert

On Thursday, January 8, 2015 12:05:00 PM UTC, Tim Watts wrote:


Can you use PIR insulation board *under* the joists - that would save
much cutting.

When you look at the separation of the joists and distance down to the earth it's often not easy to get whole thick boards down there.

Robert

On 08/01/15 12:22, RobertL wrote:
On Thursday, January 8, 2015 11:00:06 AM UTC, Adam Funk wrote:

width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

Get the special saw; it is very sharp but has no teeth.

Ooh - that sounds interesting.

On 08/01/2015 12:46, Tim Watts wrote:
On 08/01/15 12:22, RobertL wrote:
On Thursday, January 8, 2015 11:00:06 AM UTC, Adam Funk wrote:

width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

Get the special saw; it is very sharp but has no teeth.

Ooh - that sounds interesting.


AKA: bread knife :-)

--
Cheers, Rob

On 08/01/15 12:25, RobertL wrote:
On Thursday, January 8, 2015 12:05:00 PM UTC, Tim Watts wrote:


Can you use PIR insulation board *under* the joists - that would save
much cutting.

When you look at the separation of the joists and distance down to the earth it's often not easy to get whole thick boards down there.

Robert


Granted - had the same problem with my roof - had to cut the board
lenghtways in 2 halfs

On 08/01/15 13:00, RJH wrote:
On 08/01/2015 12:46, Tim Watts wrote:
On 08/01/15 12:22, RobertL wrote:
On Thursday, January 8, 2015 11:00:06 AM UTC, Adam Funk wrote:

width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

Get the special saw; it is very sharp but has no teeth.

Ooh - that sounds interesting.


AKA: bread knife :-)


Apart from small cuts, I found bread knives to be horrible - dangerous even.

The foam tends to grip the blade because the blade has no kerf to speak of.


I assumed the PP meant:

http://www.celotex.co.uk/products/accessories
Celotex Insulation Saw

which does have teeth, but claims to produce less dust.

TBH the dust is not too bad if you wear a basic mask - it's heavy and in
still air tends to fall quickly (unlike plaster dust) and be easily
hoovered. But it's horrible if you get it in the eye - feels like sand.

On Thursday, 8 January 2015 11:00:06 UTC, Adam Funk wrote:
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I would:
- cut PIR board to fit between joists
- push into place (metal side up)
- temporarily pin with a couple of nails.
- seal gap with expanding foam from a foam gun (which will also glue the
PIR in place)
This point is critical. Assuming your void is ventilated (and if not,
your joists will rot), most of the insulation effect comes from stopping
draughts.
- lather, rinse, repeat.

"Adam Funk" wrote in message
...
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I envisage nailing laths up to the joists near one end of each room,
sticking a strip/slab of fairly inflexible insulation into each gap, &
nailing more laths up & repeating as necessary to fill all the spaces
between the joists.

Does that sound right?

Is it possible (or too expensive) to get strips already in the right
width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

For the small gaps where joists are close to the side walls, should I
just stuff rockwool or something like that up in there?


The important thing is No Gaps.
Slightest gap=draught defeats all your work.
I used rigid foam cut 2cm smaller than the gaps & held temporarily with a
few nails.
Gaps filled with canned foam,

Look on the internet for "insulation+boards+seconds+locality" for a local
seller.
Seconds come half price.
Needs a few small repairs you can do with the canned foam easy.
Eg:- http://www.aandainsulationservices.com/

Foam best full depth of joist.

Any scraps, secure to walls vertically tight against your floor with foam.
Again no gaps.
Reduces thermal bridge effect of heat creeping through the brickwork.

/- push into place (metal side up) /q

Metal side up????

Jim K

On 08/01/2015 10:48, Adam Funk wrote:
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms. There are crawl spaces below them that I can sit
in, and holes (professionally made, with lintels) that I can crawl
through to get to them.

I envisage nailing laths up to the joists near one end of each room,
sticking a strip/slab of fairly inflexible insulation into each gap, &
nailing more laths up & repeating as necessary to fill all the spaces
between the joists.

Does that sound right?

Is it possible (or too expensive) to get strips already in the right
width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

For the small gaps where joists are close to the side walls, should I
just stuff rockwool or something like that up in there?

Thanks.


I'm convinced this is a worthwhile evidence, from my experience of two
downstairs floors. How you do it is, however, subject to local conditions.

The first of mine was done when replacing the entire floor and was a
fairly straightforward job of nailing roofing battens along the insides
of the joists at the bottom then dropping tight-fitting PIR boards onto
that before adding floorboards.

The second was done in situ from the low cellar under my dining room.
The pipes, cables, etc here would have made PIR almost impossible to
fit, except under the bottom faces of the joists and the headroom was
already low. Also, access would not have allowed an 8x4 board into the
space, so there would have been a lot of joints to tape over. Instead,
I pushed loft insulation into the spaces and suspended it
'hammock-style' with a zig zag of nylon string between nails (which was
largely unnecessary as it turned out as it has stayed put by friction).
The result was pretty much the same and both these rooms went from
cold to warm immediately.

I suspect that most of the benefit is due to draught-proofing/baffling
rather than isulation as such. Although I tried to fill every available
space, I didn't get paranoid about curing every possible draught,
working on the basis that 99% of the job gives 99% of the effect and the
other 1% is too much of a PITA to deal with. Undoubtedly, someone will
tell you that if you don't seal the floor hermetically the entire job is
a waste of time but experience says that simply isn't true, at least in
my case.

In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume
--
Chris French

On 2015-01-08, Andrew Gabriel wrote:

In article ,
Adam Funk writes:
Having upgraded our heating system last year, we now notice that the
kitchen & dining room still don't get very warm, although most of the
rest of the house is well-heated. I want to insulate under the floors
of those 2 rooms.

I would want to establish with some certainty that was where the heat
was being lost before putting in the effort. The floor is usually the
place least heat is lost, unless it's bare boards with gaps allowing a
draft to blow through.

Otherwise you risk putting in all the effort, and not seeing the gains
you wanted.

Interesting point. The floors in those two rooms do feel cold when we
walk on them. The kitchen is vinyl on hardboard on floorboards; the
dining room is carpet on underlay on floorboards. There's currently
no insulation in the floor, and the crawl spaces are ventilated (air
bricks). I can't think where else the heat could be going out: the 2
windows & the back door are modern double-glazed ones. I haven't been
able to feel any distinct drafts, though.

On Thursday, 8 January 2015 19:09:42 UTC, Chris French wrote:
In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume

Yup. Specifically, the foil vapour barrier needs to be on the warm side
of the insulation to avoid interstitial condensation.

On 09/01/15 13:16, Martin Bonner wrote:
On Thursday, 8 January 2015 19:09:42 UTC, Chris French wrote:
In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume

Yup. Specifically, the foil vapour barrier needs to be on the warm side
of the insulation to avoid interstitial condensation.


All the celotex I've seen is foiled on both sides.

In article ,
Tim Watts writes:
On 09/01/15 13:16, Martin Bonner wrote:
On Thursday, 8 January 2015 19:09:42 UTC, Chris French wrote:
In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume

Yup. Specifically, the foil vapour barrier needs to be on the warm side
of the insulation to avoid interstitial condensation.

All the celotex I've seen is foiled on both sides.

PIR is certainly available without a foil facing, although not so common.
Don't know about one side only.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In message , Tim Watts
writes
On 09/01/15 13:16, Martin Bonner wrote:
On Thursday, 8 January 2015 19:09:42 UTC, Chris French wrote:
In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume

Yup. Specifically, the foil vapour barrier needs to be on the warm side
of the insulation to avoid interstitial condensation.


All the celotex I've seen is foiled on both sides.

I'm sure the stuff I used to do the bathroom wall was only foil on one
side.

It had Celotex printed on the other side, on the paper or whatever it is
facing
--
Chris French

On 2015-01-08, Tim Watts wrote:

Can you use PIR insulation board *under* the joists - that would save
much cutting.

The hole into the crawl space is 65 X 60 cm, so I can't fit whole
boards into there anyway.


However, make sure the space under this all is ventilated (rather than
the air bricks/vents opening between the joists) or you'll get damp
problems.

The space under the kitchen has two air bricks to the outside & a
square hole (a bit smaller than the main one) to the space under the
dining room. That space has one air brick & the 65 X 60 cm hole to
the front cellar, which has some air bricks. The cellar is musty
(especially near the cellar floor) but all the joists are OK.

I'm inclined to think that putting the insulation between rather than
under the joists is better for ventilating the joists themselves.

On 2015-01-08, Tim Watts wrote:

On 08/01/15 13:00, RJH wrote:
On 08/01/2015 12:46, Tim Watts wrote:
On 08/01/15 12:22, RobertL wrote:
On Thursday, January 8, 2015 11:00:06 AM UTC, Adam Funk wrote:

width (14", I guess), or should I get big boards & cut them into
strips? What tools do I need to cut them?

Get the special saw; it is very sharp but has no teeth.

Ooh - that sounds interesting.


AKA: bread knife :-)


Apart from small cuts, I found bread knives to be horrible - dangerous even.

The foam tends to grip the blade because the blade has no kerf to speak of.


I assumed the PP meant:

http://www.celotex.co.uk/products/accessories
Celotex Insulation Saw

which does have teeth, but claims to produce less dust.

TBH the dust is not too bad if you wear a basic mask - it's heavy and in
still air tends to fall quickly (unlike plaster dust) and be easily
hoovered. But it's horrible if you get it in the eye - feels like sand.

(Sorry for the delay in replying to this thread --- my leafnode server
went down & has just been fixed.)

The builders who are doing some work elsewhere in our house now are
insulation enthusiasts so I've seen a lot of Celotex in the past few
days. They've been using an ordinary crosscut saw to cut it --- but
possibly (probably?) not the same one they use on timber.

On 2015-01-09, Tim Watts wrote:

On 09/01/15 13:16, Martin Bonner wrote:
On Thursday, 8 January 2015 19:09:42 UTC, Chris French wrote:
In message , JimK
writes
/- push into place (metal side up) /q

Metal side up????


Foil covered side up I assume

Yup. Specifically, the foil vapour barrier needs to be on the warm side
of the insulation to avoid interstitial condensation.


All the celotex I've seen is foiled on both sides.

All the Celotex I've seen (in the past few days) is like that too.

On 23/01/15 21:05, Adam Funk wrote:
On 2015-01-08, Tim Watts wrote:

Can you use PIR insulation board *under* the joists - that would save
much cutting.

The hole into the crawl space is 65 X 60 cm, so I can't fit whole
boards into there anyway.


However, make sure the space under this all is ventilated (rather than
the air bricks/vents opening between the joists) or you'll get damp
problems.

The space under the kitchen has two air bricks to the outside & a
square hole (a bit smaller than the main one) to the space under the
dining room. That space has one air brick & the 65 X 60 cm hole to
the front cellar, which has some air bricks. The cellar is musty
(especially near the cellar floor) but all the joists are OK.

I'm inclined to think that putting the insulation between rather than
under the joists is better for ventilating the joists themselves.


Not so relevant - the key factor is whether the air bricks are *lower*
than the bottom of the joists. You need to ventilate below the
insulation, not in the space you insulated.

On 2015-01-08, harryagain wrote:

The important thing is No Gaps.
Slightest gap=draught defeats all your work.
I used rigid foam cut 2cm smaller than the gaps & held temporarily with a
few nails.
Gaps filled with canned foam,

Look on the internet for "insulation+boards+seconds+locality" for a local
seller.
Seconds come half price.
Needs a few small repairs you can do with the canned foam easy.
Eg:- http://www.aandainsulationservices.com/

Foam best full depth of joist.

Any scraps, secure to walls vertically tight against your floor with foam.
Again no gaps.
Reduces thermal bridge effect of heat creeping through the brickwork.

Thanks (& to others) for the advice. (I've got some other irons in
the fire around the house right now, so I'm not sure when I'll get
round to this.)