Insulation in cavity or inside the room?
 

I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom and the top of the cavity insulation?

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

george

Insulation in cavity or inside the room?
 

On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

Presumably sealed in at the eves/soffits?

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom and the top of the cavity insulation?

No more so than if left uninsulated.

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

Or take the chance to do both - more overall, and less loss of internal
space.

A bit depends on what kind of occupancy. Insulation inside is good for
intermittent use spaces, since you can raise the internal temperature
quickly since its decoupled from the bulk of the thermal mass of the
masonry.

Full time occupancy can be better with more thermal mass inside the
insulation since it takes longer to slew in temperature, thus keeping
temperature swings down and reducing influence of very hot/cold days.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Insulation in cavity or inside the room?
 

On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom and the top of the cavity insulation?

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

george


Find and read a copy of Approved Doc Part L and you will find info about
perimeter insulation. New builds tend to have suspended block and beam
construction which is grouted and overlaid with PIR insulation which
minimises cold bridges at DPC level. Other methods are to have PIR
under the slab which also has a band of perimeter insulation in order to
reduce cold-bridging.

Insulation in cavity or inside the room?
 

On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom and the top of the cavity insulation?

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

george


Cavity walls came about to prevent damp in solid walls buildings. 18"
stone was fine, single skin brick on 50s was the problem.

Filling the cavity gives insulation, but it has inherent risk of damp,
there are many claims of cavity wall insulation failures - it is fine if
done properly, but would not be my choice.

Can you not build with Thermalite blocks, they are fully load bearing as
long as you put suitable wall pate on top (standard practise) and
lintols with correct bearing over any openings.

Insulation in cavity or inside the room?
 

On 06/05/2021 12:05, rick wrote:
On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom
and the top of the cavity insulation?

Wouldnt the same amount of insulation be more effective if on the
inside of the block wall ?

george


Cavity walls came about to prevent damp in solid walls buildings.Â* 18"
stone was fine, single skin brick on 50s was the problem.

Filling the cavity gives insulation, but it has inherent risk of damp,
there are many claims of cavity wall insulation failures - it is fine if
done properly, but would not be my choice.

Can you not build with Thermalite blocks, they are fully load bearing as
long as you put suitable wall pate on top (standard practise) and
lintols with correct bearing over any openings.



If BCO is involved (and legally he has to be) then he will insist that
the construction complies with Part L anyway, which probably means
thermal block inner leaf and either 50mm PIR + 50mm cavity or 100mm
full-fill cavity with rockwool batts, then 100mm outer brick skin or
100mm blockwork to be rendered.

Insulation in cavity or inside the room?
 

On Tue, 4 May 2021 21:58:05 +0100, John Rumm
wrote:

snip

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

Or take the chance to do both - more overall, and less loss of internal
space.

A close neighbour and also EOT and similar age property had the
external insulation cladding (he is the South facing end of a 10 house
terrace).

The house was sold (to the brother of the guy who lives at the other
and of the terrace) and they noticed damp in the upper flank wall.

It turns out that the tiles didn't fully cover the end of the
insulation and water was running / being blown underneath the outer
roof tiles and behind the insulation and onto (the solid brick) wall.
;-(

Now it has nowhere else to go it ends up going though the wall and
into the building. ;-(

They had some scaffolding erected and the bro from the other end did
something (replaced the end tiles for wider ones to provide more
overhang) in the hope to cure the problem that should never existed.

The problem is even if it was guaranteed work (maybe only to the
initial owner?) many people wouldn't want such people back and so fund
/ provide the remedial work themselves. ;-(

Cheers, T i m

Insulation in cavity or inside the room?
 

On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.


I'm thinking of doing the same to house a downstairs toilet/walk-in
shower. What sort of size and budget do you have in mind.

Another Dave
--
Change nospam to techie

Insulation in cavity or inside the room?
 

On 06/05/2021 14:28, Another Dave wrote:
On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.


I'm thinking of doing the same to house a downstairs toilet/walk-in
shower. What sort of size and budget do you have in mind.

Another Dave

The merits or demerits of having thermal mass (blockwork) inside the
insulation have been well discussed before. Essentially it slows the
warm up time and it slows the cool down time and may make a house a bit
cooler in summer.

It's ideal for rooms in constant use as it helps keep the temperature
even. Its bad for an occasional room that you want to warm up quickly.


--
Canada is all right really, though not for the whole weekend.

"Saki"

Insulation in cavity or inside the room?
 

I spent 2 months doing plans myself in inkscape, put them in a week ago.

Takes 2 months until i know if i can go ahead.

i have no budget worked out,
but plan to save by doingh everything myself,
except maybe fancy brickwork where the neighbours can see it.

The price of windows is frightening!

I will post more if i get planning permission

g



On Thursday, May 6, 2021 at 2:28:52 PM UTC+1, Another Dave wrote:
On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

I'm thinking of doing the same to house a downstairs toilet/walk-in
shower. What sort of size and budget do you have in mind.

Another Dave
--
Change nospam to techie

Insulation in cavity or inside the room?
 

On 07/05/2021 17:40, George Miles wrote:
I spent 2 months doing plans myself in inkscape, put them in a week ago.

Takes 2 months until i know if i can go ahead.

i have no budget worked out,
but plan to save by doingh everything myself,
except maybe fancy brickwork where the neighbours can see it.

The price of windows is frightening!

I will post more if i get planning permission


Thanks. I'm assuming it's permitted development as it's at the back of
the (detached) house, several metres from the border and only a field
behind the house. I'm not expecting too much windowing in a shower room!

I appreciate building control must be involved.

Another Dave

--
Change nospam to techie

Insulation in cavity or inside the room?
 

On 07/05/2021 19:42, Another Dave wrote:
On 07/05/2021 17:40, George Miles wrote:
I spent 2 months doing plans myself in inkscape, put them in a week ago.

Takes 2 months until i know if i can go ahead.

i have no budget worked out,
but plan to save by doingh everything myself,
except maybe fancy brickwork where the neighbours can see it.

The price of windows is frightening!

(sorry responding to the wrong post here, but can't see George's post in
my feed)

It can be worth finding a maker of them to talk to, rather that a
traditional vendor of windows. I found when I did my loft conversion[1]
I got some quotes for several thousand initially. A bit of shopping
about got that down to about £1k, then eventually I founds a window
manufacturer in Romford that was happy to supply builders etc directly,
and that got the price down to £570

[1] that was for Building Regs 2002 Part L compliant with Low E glass
and trickle vents.

Window 1 €“ clear glass (MOE) 1800mm x 1200mm:
3 panel window with outer two panels being opening casement, centre
window fixed, with fanlight to top of centre window. .

Window 2 €“ obscure glass 1200mm x 1050mm:
1 fixed window with full width fanlight to top.

Window 3 €“ clear glass 550mm x 1050mm:
1 casement window with fanlight to top.

(note those prices are 18 years old now - so ignore the absolute
numbers, and look at the differences!)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/