On 24 Dec, 00:49, fred wrote:
In article
,
RobertL writesRemember to get building control
approval (it's covered by Part L).

There is no requirement to gain approval for additional insulation where
there is no change to the structure.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."

So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.

Cheers
Richard

In article
,
geraldthehamster writes
On 24 Dec, 00:49, fred wrote:
In article
,
RobertL writesRemember to get building control
approval (it's covered by Part L).

There is no requirement to gain approval for additional insulation where
there is no change to the structure.

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."

So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.

Agreed, thanks for pointing out the exact wording that makes it far
clearer.

When I did mine I worked below from an existing hatch but in one area
had to lift a few board to do the poke fill method which (even if I was
bothered) shouldn't have required a notice.

Although it's been suggested here, I wouldn't lift all the boards,
vapour barrier considerations or not.

It's wise to take care if there is a compliance bod in the vicinity.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

geraldthehamster wrote:
On 22 Dec, 10:32, stuart noble wrote:
On 22/12/2010 09:46, RobertL wrote:



On Dec 20, 12:31 pm, wrote:
I plan to redirect our ground floor front room next year.
Currently, the walls are unplastered, and we've rewired so floorboards
are loose, so any option is possible at this point.
My question is what, if anything to do about draughts from under the
floor.
The house is Victorian, and slightly raised with large cavities under
the floor-boards. There is also a metal decorated air-grill at the
front of our house which ventilates the space under this room.
We were in the same situation and I didn't put celotex under the
floor; I wish I had done. We did fill the gaps between the
floorboards using a V section platic strip designed for the purpose.
That helped a lot.
My advice: do a proper insulation job between the joists and leave the
ventilation under there alone. Remember to get building control
approval (it's covered by Part L).
Sod that- Hide quoted text -

- Show quoted text -

Seconded. Celotex is expensive enough without unnecessary fees.


Not only that, but once the BCO is involved it has to be to latest spec,
or not at all.

He has no wriggle room for you to say 'but this is at least better than
it was'

This is a glaring problem for people trying to save power.


Cheers
Richard

fred wrote:
In article
,
RobertL writes
Remember to get building control
approval (it's covered by Part L).

There is no requirement to gain approval for additional insulation where
there is no change to the structure.

That depends on whether you call adding insulation a 'material change'
or not.


Since insulation is fully covered in the regulations, it would seem
likely that it is so considered.

Tabby wrote:
On Dec 21, 1:07 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 20, 5:37 pm, Ronald Raygun
wrote:
Tabby wrote:
Don't block the vents, unless you want the whole floor structure to
slowly rot away. The ideal thing t do is lift floorboards, fit
insulation between joists, add a VB over the top and re-lay the
boards.
I don't think that's a good idea. The whole point of under floor
ventilation is to eliminate stagnant air which promotes rot, which
affects not only the joists but the floorboards as well. If you're
going to wrap (even just the under-side of) the floorboards in a vapour
proof skin, you are *creating* pockets of stagnant air, defeating the
purpose of the ventilation, thereby putting the floor boards at risk.
You need to remember that a certain amount of draught is actually a
good thing, otherwise the room becomes too stuffy.
The not so ideal thing is to jsut rely on underlay to stop
drafts and not have insulation - but it sounds like now is as good a
time as any to insulate it.
I think it's best not to insulate with anything non-permeable. Use
underlay if you must, but with beautifully varnished floorboards, the
in-character thing is to have rugs, not wall-to-wall carpet. With rugs
you don't want an underlay that's too thick, or you'll keep tripping over
the rug edges. Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking
the gaps with ordinary string may be effective.
The point of underfloor ventilation is to conduct away the damp that
evaporates from the earth below,
No, it is not. Or only in part.

once damp HAS evaporated, it gets very dry under a house. Oddly enough,
this is something to do with rain not falling on it.

If you have wet soil under a house, you have a drainage problem.

so RH doesnt rise high enough to

cause rot. If you insulate between the josits with no VB, you'd be
right, condensation and rot could occur. But with insulation and VB
above all is well.
correct.



NT

The reason to elevate timber floors is to avoid damp from the ground.
Timber floors laid straight on ground, only occasionally encountered,
tend to rot.


but who can say if that is from upwards moisture from the ground, or
downwards condensing ON the ground?





NT

On 24 Dec,
geraldthehamster wrote:

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."

So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.

Hasn't it to be more than 25% of the element to be notifiable? You did some
last year and some the year before etc. didn't you?

--
B Thumbs
Change lycos to yahoo to reply

"fred" wrote in message ...
Agreed, thanks for pointing out the exact wording that makes it far
clearer.

When I did mine I worked below from an existing hatch but in one area had
to lift a few board to do the poke fill method which (even if I was
bothered) shouldn't have required a notice.

Although it's been suggested here, I wouldn't lift all the boards, vapour
barrier considerations or not.

It's wise to take care if there is a compliance bod in the vicinity.
--

However, I have not heard a word suggesting that this will happen or not
happen

On 24 Dec, 12:55, wrote:
On 24 Dec, *
* * *geraldthehamster wrote:

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."

So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.

Hasn't it to be more than 25% of the element to be notifiable? You did some
last year and some the year before etc. didn't you?

--
* B Thumbs
* Change lycos to yahoo to reply

Yes, but it's 25% of that element, not of all the elements of that
type in the house. ie if you expose more than a quarter of the floor
in one room. It's all academic anyway, who the hell is going to notify
Building Control if they're insulating a floor, and what are Building
Control going to do anyway, tell you to take it out again? Really not
worth worrying about.

Cheers
Richard

geraldthehamster wrote:
On 24 Dec, 12:55, wrote:
On 24 Dec,
geraldthehamster wrote:

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."
So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.
Hasn't it to be more than 25% of the element to be notifiable? You did some
last year and some the year before etc. didn't you?

--
B Thumbs
Change lycos to yahoo to reply

Yes, but it's 25% of that element, not of all the elements of that
type in the house. ie if you expose more than a quarter of the floor
in one room. It's all academic anyway, who the hell is going to notify
Building Control if they're insulating a floor, and what are Building
Control going to do anyway, tell you to take it out again? Really not
worth worrying about.


Basically talked this over with a mate, who is doing up house to sell
when things improve.. No BCO, no ticket. No ticket no resale value increase.

No insulation!

Cheers
Richard

On 25/12/10 02:56, The Natural Philosopher wrote:
geraldthehamster wrote:
On 24 Dec, 12:55, wrote:
On 24 Dec, geraldthehamster wrote:

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."
So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.
Hasn't it to be more than 25% of the element to be notifiable? You
did some
last year and some the year before etc. didn't you?

--
B Thumbs
Change lycos to yahoo to reply

Yes, but it's 25% of that element, not of all the elements of that
type in the house. ie if you expose more than a quarter of the floor
in one room. It's all academic anyway, who the hell is going to notify
Building Control if they're insulating a floor, and what are Building
Control going to do anyway, tell you to take it out again? Really not
worth worrying about.


Basically talked this over with a mate, who is doing up house to sell
when things improve.. No BCO, no ticket. No ticket no resale value
increase.

No insulation!

I never understand this - I don't fix houses for resale value, I fix it
so I like it...

In your mate's case, if there really was a resale value potential
increase, and he felt the BNA sign off was actually worth something, why
not just get a BNA - for that value of work it would only be a couple of
hundred?

--
Tim Watts

On Dec 24, 12:24*pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 21, 1:07 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 20, 5:37 pm, Ronald Raygun
wrote:
Tabby wrote:
Don't block the vents, unless you want the whole floor structure to
slowly rot away. The ideal thing t do is lift floorboards, fit
insulation between joists, add a VB over the top and re-lay the
boards.
I don't think that's a good idea. *The whole point of under floor
ventilation is to eliminate stagnant air which promotes rot, which
affects not only the joists but the floorboards as well. *If you're
going to wrap (even just the under-side of) the floorboards in a vapour
proof skin, you are *creating* pockets of stagnant air, defeating the
purpose of the ventilation, thereby putting the floor boards at risk..
You need to remember that a certain amount of draught is actually a
good thing, otherwise the room becomes too stuffy.
The not so ideal thing is to jsut rely on underlay to stop
drafts and not have insulation - but it sounds like now is as good a
time as any to insulate it.
I think it's best not to insulate with anything non-permeable. *Use
underlay if you must, but with beautifully varnished floorboards, the
in-character thing is to have rugs, not wall-to-wall carpet. *With rugs
you don't want an underlay that's too thick, or you'll keep tripping over
the rug edges. *Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking
the gaps with ordinary string may be effective.
The point of underfloor ventilation is to conduct away the damp that
evaporates from the earth below,
No, it is not. Or only in part.

once damp HAS evaporated, it gets very dry under a house. Oddly enough,
this is something to do with rain not falling on it.

If you have wet soil under a house, you have a drainage problem.

* so RH doesnt rise high enough to

cause rot. If you insulate between the josits with no VB, you'd be
right, condensation and rot could occur. But with insulation and VB
above all is well.
correct.

NT

The reason to elevate timber floors is to avoid damp from the ground.
Timber floors laid straight on ground, only occasionally encountered,
tend to rot.

but who can say if that is from upwards moisture from the ground, or
downwards condensing ON the ground?

Maybe both. The ground is always damp though, in Britain. Even when it
looks dry it isnt really.


NT

Tim Watts wrote:
On 25/12/10 02:56, The Natural Philosopher wrote:
geraldthehamster wrote:
On 24 Dec, 12:55, wrote:
On 24 Dec, geraldthehamster wrote:

Approved Document L1B, 5.7 b. i. defines the replacement of an
existing layer as "stripping down the element to expose the basic
structural components (brick/blockwork, timber/metal frame, joists,
rafters, etc)..."
So I guess if you take up the floorboards, strictly speaking it's
notifiable. I wouldn't bother, and I bet nobody has.
Hasn't it to be more than 25% of the element to be notifiable? You
did some
last year and some the year before etc. didn't you?

--
B Thumbs
Change lycos to yahoo to reply

Yes, but it's 25% of that element, not of all the elements of that
type in the house. ie if you expose more than a quarter of the floor
in one room. It's all academic anyway, who the hell is going to notify
Building Control if they're insulating a floor, and what are Building
Control going to do anyway, tell you to take it out again? Really not
worth worrying about.


Basically talked this over with a mate, who is doing up house to sell
when things improve.. No BCO, no ticket. No ticket no resale value
increase.

No insulation!

I never understand this - I don't fix houses for resale value, I fix it
so I like it...

In your mate's case, if there really was a resale value potential
increase, and he felt the BNA sign off was actually worth something, why
not just get a BNA - for that value of work it would only be a couple of
hundred?

He hasn't got even a couple of hundred.

And the estate agent was dubious as to whether even so, it would
increase the house value.

Tabby wrote:
On Dec 24, 12:24 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 21, 1:07 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 20, 5:37 pm, Ronald Raygun
wrote:
Tabby wrote:
Don't block the vents, unless you want the whole floor structure to
slowly rot away. The ideal thing t do is lift floorboards, fit
insulation between joists, add a VB over the top and re-lay the
boards.
I don't think that's a good idea. The whole point of under floor
ventilation is to eliminate stagnant air which promotes rot, which
affects not only the joists but the floorboards as well. If you're
going to wrap (even just the under-side of) the floorboards in a vapour
proof skin, you are *creating* pockets of stagnant air, defeating the
purpose of the ventilation, thereby putting the floor boards at risk.
You need to remember that a certain amount of draught is actually a
good thing, otherwise the room becomes too stuffy.
The not so ideal thing is to jsut rely on underlay to stop
drafts and not have insulation - but it sounds like now is as good a
time as any to insulate it.
I think it's best not to insulate with anything non-permeable. Use
underlay if you must, but with beautifully varnished floorboards, the
in-character thing is to have rugs, not wall-to-wall carpet. With rugs
you don't want an underlay that's too thick, or you'll keep tripping over
the rug edges. Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking
the gaps with ordinary string may be effective.
The point of underfloor ventilation is to conduct away the damp that
evaporates from the earth below,
No, it is not. Or only in part.
once damp HAS evaporated, it gets very dry under a house. Oddly enough,
this is something to do with rain not falling on it.
If you have wet soil under a house, you have a drainage problem.
so RH doesnt rise high enough to
cause rot. If you insulate between the josits with no VB, you'd be
right, condensation and rot could occur. But with insulation and VB
above all is well.
correct.
NT
The reason to elevate timber floors is to avoid damp from the ground.
Timber floors laid straight on ground, only occasionally encountered,
tend to rot.
but who can say if that is from upwards moisture from the ground, or
downwards condensing ON the ground?

Maybe both. The ground is always damp though, in Britain. Even when it
looks dry it isnt really.

You haven't been under a house then?

Usually bone dry unless there is some sort of water table there.



NT

On 25/12/10 12:12, The Natural Philosopher wrote:
He hasn't got even a couple of hundred.

And the estate agent was dubious as to whether even so, it would
increase the house value.

I guess that brings it back to - do it if *you* want to and stop
thinking about estate agents

--
Tim Watts

On Dec 25, 12:13*pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 24, 12:24 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 21, 1:07 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 20, 5:37 pm, Ronald Raygun
wrote:
Tabby wrote:
Don't block the vents, unless you want the whole floor structure to
slowly rot away. The ideal thing t do is lift floorboards, fit
insulation between joists, add a VB over the top and re-lay the
boards.
I don't think that's a good idea. *The whole point of under floor
ventilation is to eliminate stagnant air which promotes rot, which
affects not only the joists but the floorboards as well. *If you're
going to wrap (even just the under-side of) the floorboards in a vapour
proof skin, you are *creating* pockets of stagnant air, defeating the
purpose of the ventilation, thereby putting the floor boards at risk.
You need to remember that a certain amount of draught is actually a
good thing, otherwise the room becomes too stuffy.
The not so ideal thing is to jsut rely on underlay to stop
drafts and not have insulation - but it sounds like now is as good a
time as any to insulate it.
I think it's best not to insulate with anything non-permeable. *Use
underlay if you must, but with beautifully varnished floorboards, the
in-character thing is to have rugs, not wall-to-wall carpet. *With rugs
you don't want an underlay that's too thick, or you'll keep tripping over
the rug edges. *Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking
the gaps with ordinary string may be effective.
The point of underfloor ventilation is to conduct away the damp that
evaporates from the earth below,
No, it is not. Or only in part.
once damp HAS evaporated, it gets very dry under a house. Oddly enough,
this is something to do with rain not falling on it.
If you have wet soil under a house, you have a drainage problem.
* so RH doesnt rise high enough to
cause rot. If you insulate between the josits with no VB, you'd be
right, condensation and rot could occur. But with insulation and VB
above all is well.
correct.
NT
The reason to elevate timber floors is to avoid damp from the ground.
Timber floors laid straight on ground, only occasionally encountered,
tend to rot.
but who can say if that is from upwards moisture from the ground, or
downwards condensing ON the ground?

Maybe both. The ground is always damp though, in Britain. Even when it
looks dry it isnt really.

You haven't been under a house then?

Usually bone dry unless there is some sort of water table there.



NT

Chuck a piece of plastic membrane down, come back next day and you'll
have a wet patch under it.


NT

Tim Watts wrote:
On 25/12/10 12:12, The Natural Philosopher wrote:
He hasn't got even a couple of hundred.

And the estate agent was dubious as to whether even so, it would
increase the house value.

I guess that brings it back to - do it if *you* want to and stop
thinking about estate agents

In his case it was simple cost benefit. He's been ill for years and cant
do full time work. Wife works in estate agents, retirement looms, kids
gone, so everything is 'what is the least amount of money I can spend
using my spare time to maximise the nest egg'

Cost benefit of underfloor insulation was negative, on best advice.

In terms of resale value.

We all agree in terms of heating bills and comfort its a winner all the way.

Tabby wrote:
On Dec 25, 12:13 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 24, 12:24 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 21, 1:07 pm, The Natural Philosopher
wrote:
Tabby wrote:
On Dec 20, 5:37 pm, Ronald Raygun
wrote:
Tabby wrote:
Don't block the vents, unless you want the whole floor structure to
slowly rot away. The ideal thing t do is lift floorboards, fit
insulation between joists, add a VB over the top and re-lay the
boards.
I don't think that's a good idea. The whole point of under floor
ventilation is to eliminate stagnant air which promotes rot, which
affects not only the joists but the floorboards as well. If you're
going to wrap (even just the under-side of) the floorboards in a vapour
proof skin, you are *creating* pockets of stagnant air, defeating the
purpose of the ventilation, thereby putting the floor boards at risk.
You need to remember that a certain amount of draught is actually a
good thing, otherwise the room becomes too stuffy.
The not so ideal thing is to jsut rely on underlay to stop
drafts and not have insulation - but it sounds like now is as good a
time as any to insulate it.
I think it's best not to insulate with anything non-permeable. Use
underlay if you must, but with beautifully varnished floorboards, the
in-character thing is to have rugs, not wall-to-wall carpet. With rugs
you don't want an underlay that's too thick, or you'll keep tripping over
the rug edges. Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking
the gaps with ordinary string may be effective.
The point of underfloor ventilation is to conduct away the damp that
evaporates from the earth below,
No, it is not. Or only in part.
once damp HAS evaporated, it gets very dry under a house. Oddly enough,
this is something to do with rain not falling on it.
If you have wet soil under a house, you have a drainage problem.
so RH doesnt rise high enough to
cause rot. If you insulate between the josits with no VB, you'd be
right, condensation and rot could occur. But with insulation and VB
above all is well.
correct.
NT
The reason to elevate timber floors is to avoid damp from the ground.
Timber floors laid straight on ground, only occasionally encountered,
tend to rot.
but who can say if that is from upwards moisture from the ground, or
downwards condensing ON the ground?
Maybe both. The ground is always damp though, in Britain. Even when it
looks dry it isnt really.
You haven't been under a house then?

Usually bone dry unless there is some sort of water table there.



NT

Chuck a piece of plastic membrane down, come back next day and you'll
have a wet patch under it.


On top of it.

Condensation.

Dew



NT

On 20 Dec, 12:31, Jim wrote:
I plan to redirect our ground floor front room next year.

Currently, the walls are unplastered, and we've rewired so floorboards
are loose, so any option is possible at this point.

My question is what, if anything to do about draughts from under the
floor.

We live at a T junction, with a road running off our road straight in
front of our house. This road is a bit of a wind tunnel, and the room
we plan to decorate gets the brunt of it.

The house is Victorian, and slightly raised with large cavities under
the floor-boards. There is also a metal decorated air-grill at the
front of our house which ventilates the space under this room.

Net result is that it is seriously cold and draughty at the moment,
and I can feel quite strong cold draughts if I put my hands over the
floorboard gaps in this room.

When we've decorated the room, I plan to get an underlayed berber
style carpet, which should prevent the draughts, but I'd like it to be
as cosy as possible for my children.

Is there anything else I can do to improve insulation/carpet warmth?

I presume blocking up the air vent completely would be a bad thing? Is
it worthwhile attempting any other sort of under-floor insulation?

Thanks for your input.

There has been an awful lot of misinformation and with some small
amount of good corrections.
It is best to insulate. Do so such that the timber remains warm and
thus not at risk of condensation. If it is warm it does not need
ventilation of the sub-floor airvents but they should be left in
regardless for keeping moisture levels low in the abutting masonry and
oversite.
This is what I would recommend on our pro bono terms.
lift all fbs labelling so they go back in same places
use a proper floorboard lifter if you can hire or or borrow one
if not use long long levers with flat iron heads
glue any that split

When lifting use a hammer and fulcrum to knock them out with the nails
rather than trying to lift the nailed boards up direct (like knocking
the other end of a see saw)
Put in polythene sheeting on the oversite and put on some sand to keep
it down in place (reduces water vapour entry into void)

put in PU 4" foam with a careful cut filling any gaps with foam gun
get under and put one or two inches of foil-backed PU under the lot
cross ways using large plastic washers and long enough nails (or
battens) and leave just a small hole for you to get up back inside and
then put the last bit in and hold it up with string or whatever from
the inside
fill the last gap between FBs
put on a vapour check such as thin poly
Fbs back down either in right places or cramped together with a
replacement to take up the slack

Job done Wall plates not at risk if on a DPC joists all warm - you
warm as toast

can have boards or carpet as you wish
U Value probably (guess) 0.25 bobs yer uncle

no decay risk from oversite

chris

On 25 Dec, 16:45, chris wrote:
On 20 Dec, 12:31, Jim wrote:





I plan to redirect our ground floor front room next year.

Currently, the walls are unplastered, and we've rewired so floorboards
are loose, so any option is possible at this point.

My question is what, if anything to do about draughts from under the
floor.

We live at a T junction, with a road running off our road straight in
front of our house. This road is a bit of a wind tunnel, and the room
we plan to decorate gets the brunt of it.

The house is Victorian, and slightly raised with large cavities under
the floor-boards. There is also a metal decorated air-grill at the
front of our house which ventilates the space under this room.

Net result is that it is seriously cold and draughty at the moment,
and I can feel quite strong cold draughts if I put my hands over the
floorboard gaps in this room.

When we've decorated the room, I plan to get an underlayed berber
style carpet, which should prevent the draughts, but I'd like it to be
as cosy as possible for my children.

Is there anything else I can do to improve insulation/carpet warmth?

I presume blocking up the air vent completely would be a bad thing? Is
it worthwhile attempting any other sort of under-floor insulation?

Thanks for your input.

There has been an awful lot of misinformation and with some small
amount of good corrections.
It is best to insulate. *Do so such that the timber remains warm and
thus not at risk of condensation. If it is warm it does not need
ventilation of the sub-floor airvents but they should be left in
regardless for keeping moisture levels low in the abutting masonry and
oversite.
This is what I would recommend on our pro bono terms.
lift all fbs labelling so they go back in same places
use a proper floorboard lifter if you can hire or or borrow one
if not use long long levers with flat iron heads
glue any that split

When lifting use a hammer and fulcrum to knock them out with the nails
rather than trying to lift the nailed boards up direct (like knocking
the other end of a see saw)
Put in polythene sheeting on the oversite and put on some sand to keep
it down in place (reduces water vapour entry into void)

put in PU 4" foam with a careful cut filling any gaps with foam gun
get under and put one or two inches of foil-backed PU under the lot
cross ways using large plastic washers and long enough nails (or
battens) and leave just a small hole for you to get up back inside and
then put the last bit in and hold it up with string or whatever from
the inside
fill the last gap between FBs
put on a *vapour check such as thin poly
Fbs back down either in right places or cramped together with a
replacement to take up the slack

Job done Wall plates not at risk if on a DPC joists all warm - you
warm as toast

can have boards or carpet as you wish
U Value probably (guess) 0.25 *bobs yer uncle

no decay risk from oversite

chris- Hide quoted text -

- Show quoted text -

Blimey, talk about putting the OP off. Yes, if you wanted to rip up
your entire floor and get underneath it, and had an unlimited budget
for PU boards, you could do all that. Theoretically you'd eliminate
cold bridging across the joists, but really I don't think you'd feel
the benefit under floor of 6 inches of PU board (which is closer to
the standard for rafters, not floors), as opposed to 2 inches of board
or a roll of space blanket between the joists.

Cheers
Richard