Questions on internal and external insulation

[Red15]

Hi everyone, I'm in a dilemma,.

I'm planning on starting some renovation works on my house, the original and biggest part of the house is roughly 100 years old, it has no cavity wall and no insulation, the extension at the back is around 15 years old and has cavity wall insulation.

I am going to be pulling my house apart to look at issues with water penetrating in around the inner reveals of the living room window and from the front door reveal

Im also planning on having some rewiring, new radiators, new flooring etc. Done so to insulate internally is not an issue with regards to creating a mess etc.

So first question:-
If I can I would like to improve my EPC rating which is currently an E, what thickness of insulation would I have to go to on the internal walls to achieve this? And if I carry out the work myself how do I get the EPC rating approved?

Second question:-
Do I have to leave an air gap/cavity?
I was debating on whether to double batten the walls (50mm) and tightly pack kingspan boards between them before plasterboarding, does it matter that there'd be no air gap and that the insulation boards would tightly fitted between the wall and plasterboard?

If not I was originally thinking about battening the walls and fixing 52mm insulated plasterboards to it, is that sufficient thickness or would I need to go thicker to improve the EPC rating?

(All bearing in mind I'd want achieve the best thermal improvement possible while taking the least amount of space out of the room)

Then I was thinking about External Insulation

My worry with external is that my house is an end of terrace and the roof on the gable end does not have much of a overhang at all, theres no soffit, the fascia fits tightly against the wall, meaning the external insulation would stick out further than the roof does.
This makes me think that water could get inbetween the insulation and the main wall which could lead to damp problems inside the house.
I spoke with a contractor about it and he said it does'nt matter about the overhang as the insulation is capped off at the top anyway but I'm apprehensive.

The other thing is that what if I decide to replace my windows in 10 years time, how much damage to the insulation/render will be caused around the reveal and sill and will it be easy enough to repair?

What would you do if you were in my shoes?

 

[Diver Fred]

So to answer your first question;
Pt 1 - I understand the target is 100mm of PIR.
Pt 2, - Take photo's every step off the way; bare wall, wall prep, Insulation up Insulation partly covered, completely covers and plastered, Keep and show receipts with the 'photos.

You also need to think about ventilation - I've found that having had a cottage insulated that we are see an increase in signs of damp unless we run a dehumidifier regularly.

 

[mrrusty]

Pt 1 - I understand the target is 100mm of PIR.

I have an EPC C on a 1902 with 60mm PIR, but we do have a 50mm cavity as well. I would not install internal insulation without a ventilated cavity because IMHO this is needed to carry away any interstitial condensation. This is similar to the way a timber frame house is constructed where there is an insulated timber frame, then a ventilated cavity then the external skin of cladding, brick, rendered block etc.

Unless you could completely isolate the wall structure from internal air (unlikely), internal insulation WILL allow the wall structure behind the insulation to be cold enough to condense "room" air. Dew point of typical 20-22 degrees, 60% RH air is in the order of 12-13 degrees, so you have to plan to evaporate this inevitable condensation that will occur when conditions are right. This "drying" process can only occur when there is moving, non-saturated air across the condensate - i.e. ventilation. (which is why clothes hung outside don't dry on a still, cold day - you need the wind)

 

[Mr Chibs]

50mm insulation will make a massive difference, but won't be 'regs' compliant.
To add thermal elements to your home, you need to pay the council their fee but not if only renovating 25% of a space.

For old properties with possibility of damp, Kingspan recommended using battens and applying insulation to the battens, this is what I did, and all has been well. It's not popular on this forum, most prefer applying direct to wall no gap. What's right, what's wrong, who knows.

If you want to keep as much space, then foaming direct to the wall, is the what you probably need.

Insulate your floors too, rockwool can be used, but you need twice the depth as foam boards.

Take your time, buy a foam gun, seal gaps, tape up all joints. All will be good.

 

[mrrusty]

you need to pay the council their fee

Personally I wouldn't bother. I had an extension going on under BC and I asked our LA BC if I needed to include all the insulation work in the main house. He replied that as far as he was concerned, if I wasn't altering the wall itself (brickwork) the plaster and any insulation were just "decoration" and he wasn't interested. Other LAs may well take a different view, but this does illustrate how this is subjective.

 

[Red15]

Thanks for the replies so far, everyone seems to have a different opinion regarding EWI and IWI

 

[Mr Chibs]

IWI and EWI are two different beasts.

EWI (external wall insulation, not what I have) is probably better, as you have the brick walls acting as a thermal store, but will take longer to warm up and ou will need to render the outside, so house will look newer and it's expensive, and the rendering is not a diy job.

Neighbour was quoted around £16K to do his, being in his 80's he decided the payback would take too long.

 

[Diver Fred]

EWI (external wall insulation, not what I have) is probably better, as you have the brick walls acting as a thermal store, but will take longer to warm up and ou will need to render the outside, so house will look newer and it's expensive, and the rendering is not a diy job.

Neighbour, builder by trade externally insulated his bungalow. He covered the EWI with larch planking. (From brickwork, insulation, joints taped up, sealed top and bottom, membrane, battered air gap, larch sheath. I
He tells me it works well and the house does look good.

my cottage has EWI, rendered finish. Does keep clean but was professionally done.

 

[George_engineer]

IWI and EWI are two different beasts.

EWI (external wall insulation, not what I have) is probably better, as you have the brick walls acting as a thermal store, but will take longer to warm up and ou will need to render the outside, so house will look newer and it's expensive, and the rendering is not a diy job.

Neighbour was quoted around £16K to do his, being in his 80's he decided the payback would take too long.

While it's an individual choice of course, payback should only be part of the consideration. Insulated homes are just nicer to live in, with far less dramatic fluctuations in temperature and condensation/humidity. That insulation also (eventually) pays for itself is just a bonus, really.

 

[jeds]

EWI can look awful and presents issues with openings, window sills, and matching into eaves overhangs and adjoining properties. Otherwise it is the least disruptive and will achieve a fairly predictable result.

IWI is disruptive (which may not be an issue, considering the scope of works you have planned) and has the advantage of not altering the external look of the house. It also provides a faster thermal response, which means you turn your heating on and it gets warm very quickly but it also cools quicker. This is ideal if you have more of an irregular lifestyle and aren't home all the time.

From your description I would go with IWI using PIR thermal laminate plasterboard. You can go room by room as and when you complete your works. 52.5 should be your minimum, but also consider 62.5 or 72.5. Fixing depends what you are fixing to? What sort of plaster do you have at present and how easily could it be removed?

PS, when comparing costs, make sure you compare like for like. Don't compare PIR board with XP board, which will be considerably cheaper.

If your house is brick, the current u-value is approx 1.72. Add 52.5 it will be 0.38. Add 62.5 it will be 0.32. Add 72.5 it will be 0.28. Neither of these complies with regs but all will make a massive difference.

You could commission a non-registered EPC from any local provider and ask him/her to prepare two or three options. One for the existing, one for 52.5, one for 62.5 - etc.

 

[Red15]

EWI can look awful and presents issues with openings, window sills, and matching into eaves overhangs and adjoining properties. Otherwise it is the least disruptive and will achieve a fairly predictable result.

IWI is disruptive (which may not be an issue, considering the scope of works you have planned) and has the advantage of not altering the external look of the house. It also provides a faster thermal response, which means you turn your heating on and it gets warm very quickly but it also cools quicker. This is ideal if you have more of an irregular lifestyle and aren't home all the time.

From your description I would go with IWI using PIR thermal laminate plasterboard. You can go room by room as and when you complete your works. 52.5 should be your minimum, but also consider 62.5 or 72.5. Fixing depends what you are fixing to? What sort of plaster do you have at present and how easily could it be removed?

PS, when comparing costs, make sure you compare like for like. Don't compare PIR board with XP board, which will be considerably cheaper.

If your house is brick, the current u-value is approx 1.72. Add 52.5 it will be 0.38. Add 62.5 it will be 0.32. Add 72.5 it will be 0.28. Neither of these complies with regs but all will make a massive difference.

You could commission a non-registered EPC from any local provider and ask him/her to prepare two or three options. One for the existing, one for 52.5, one for 62.5 - etc.

Thanks for your input,
Couple of questions... why would I need to remove plaster? Could'nt I just fix battens straight to the existing plastered walls and then screw insulated plasterboard straight to them?
Also why would'nt any of those comply to building regs? What does the U-value have to be to comply?

 

[jeds]

You don't have to remove plaster, it just determines the best options for fixing thermal laminate board. For example; had your existing walls been dot and dab board, then the best option would be to remove and fix laminate dot and dab. It might still be worth considering removal if the plaster is lime based and removes very easily? If it is solid wet plaster it would likely be very difficult to remove so a lining would be the best option.

Minimum u-value for walls is currently 0.18. To achieve that you would need 100mm PIR. There isn't a laminate with 100mm PIR so you'd have to go to a lining method.