Loft insulation and air source heat pump

[anxiouscat]

I currently have an LPG boiler that is approximately 12 years old, and having a few issues so needing replacement in the next year or so. I am considering replacing it with an air source heat pump. Part of the grant + loan process for this with Home Energy Scotland requires me to get loft insulation installed. Currently, my loft is floored (really old wood, quite possibly original (old stone house, built in about 1850) or at least installed many, many years ago!) and there is a cavity between the ceiling and this old floor. A company I had out to quote for the insulation said that the insulation needs to be in that cavity, otherwise the cold air circulating in the cavity would reduce the effectiveness of the heat pump. So, they are proposing to remove the old floor, put in the insulation, and then (if I choose) put in new loft flooring on loft legs.

The insulation material they would use is Knauf Mineral Wool - does anyone have experience with this, and whether it is a good option for maintaining some ventilation in the loft to ensure no damp issues down the line. The company has said that they would ensure that they don't block ventilation from under the eaves.

Part of me is also worried about ripping up such an old loft floor, that doing so might somehow disturb some delicate balance and create (or reveal hidden) issues. Or am I just being way too anxious?!

 

[paulc]

Have a mix of mineral wool and fibreglass insulation up in my loft. Of all the insulating measures I've undertaken, it has been the most effective and produced a big improvement. Two key points: Make sure it goes right up to the walls, and fit an insulated loft hatch that has a decent draught seal.

I used XL legs when boarding out the loft (only have 3x2" joists up there). Even with insulation up against the bottom of the boards, I've not noticed any issues with damp forming.

 

[anxiouscat]

Thanks Paul, that's good to know that it's been so effective and no issues with damp for you. The quote says they will use "18mm moisture resistant chipboard, supported on 175mm Loft Legs" (not sure if that's equivalent to XL loft legs?) - I do like that they've specified "moisture-resistant"!)

 

[paulc]

175mm is standard length. XL are 300mm which gives lots more space for insulation.
As for the boards, I just used the standard ones from Wickes ('cos they did free delivery). No idea if they are moisture resistant or not.

 

[anxiouscat]

Thanks for the clarification. That's something I'll check with them then to see why they've gone with 175mm and whether XL would be better for my situation.

 

[Cubist]

Has the installer discussed how the insulation will handle moisture migrating through the ceiling below and also how the remaining void up to the boards would be ventilated?

 

[anxiouscat]

Has the installer discussed how the insulation will handle moisture migrating through the ceiling below and also how the remaining void up to the boards would be ventilated?

Do you mean moisture coming through from the house into the loft space? Or moisture from the loft space travelling through the ceiling into the house? (Either way, no, they haven't mentioned that, or how the remaining void would be ventilated - more questions to add to the list to ask them, plus also the person coming to do a comparative quote! Thank you for helping me know what to check!)

 

[Cubist]

From the rooms below the ceilings. The ceiling will capture some of the heat and moisture from the air circulating in those rooms and the colder atmosphere in the void above then helps to draw it through. If insulation material is not breathable and no room is left for air to circulate above the insulation and below the floorboards there is a risk of damp accumulating in the timbers.

 

[anxiouscat]

From the rooms below the ceilings. The ceiling will capture some of the heat and moisture from the air circulating in those rooms and the colder atmosphere in the void above then helps to draw it through. If insulation material is not breathable and no room is left for air to circulate above the insulation and below the floorboards there is a risk of damp accumulating in the timbers.

Ah, thanks for clarifying. I'll definitely ask them that.

 

[LKSF]

I currently have an LPG boiler that is approximately 12 years old, and having a few issues so needing replacement in the next year or so. I am considering replacing it with an air source heat pump. Part of the grant + loan process for this with Home Energy Scotland requires me to get loft insulation installed. Currently, my loft is floored (really old wood, quite possibly original (old stone house, built in about 1850) or at least installed many, many years ago!) and there is a cavity between the ceiling and this old floor. A company I had out to quote for the insulation said that the insulation needs to be in that cavity, otherwise the cold air circulating in the cavity would reduce the effectiveness of the heat pump. So, they are proposing to remove the old floor, put in the insulation, and then (if I choose) put in new loft flooring on loft legs.

The insulation material they would use is Knauf 1. Mineral Wool - does anyone have experience with this? and whether it is a good option for maintaining some ventilation in the loft to ensure no damp issues down the line. The company has said that they would ensure that they don't block ventilation from under the eaves.

Part of me is also worried about ripping up such an old loft floor, that doing so might somehow disturb some delicate balance and create (or reveal hidden) issues. Or 2. am I just being way too anxious?!

1. Given it's the most used loft insulation in the UK and has been for decades I think almost every household has experience of it. It's the best material for the job.

2. Yes.

It's up to you to cut down on the amount of water vapour in the house by ventilating it when and where necessary. The more you do that, the less problems you will have.

 

[Lacan07]

Ah, thanks for clarifying. I'll definitely ask them that.

Ideally for an old house you'd be using sheeps wool insulation but its considerably (predictably) more expensive. There's also another breathable product called Thermofloc (recycled paper) which is cheaper with better 'U' value.

 

[anxiouscat]

Ideally for an old house you'd be using sheeps wool insulation but its considerably (predictably) more expensive. There's also another breathable product called Thermofloc (recycled paper) which is cheaper with better 'U' value.

Sheep's wool would be great, but yes, sadly out of budget. I'll have a look into Thermofloc, thank you.

 

[fernicarry]

Thermofloc is great for awkward shaped spaces. Its very dusty so best used where its not likely to be disturbed afterwards.

Make sure it goes right up to the walls

Depends on how your internal walls are lined. Common construction method in Scotland is to have the plaster stood off the masonry on studs creating a cavity behind. This creates a capillary break in the same way a cavity wall does. If your walls are like that then you should leave the insulation just short of the external walls so that air can still circulate around the cavity and wick away any moisture than penetrates the masonry.

I'd be amazed if loft insulation alone was enough to make a HP viable for your building. Does the installer propose any other improvements? Of course if you don't already have loft insulation then you should absolutely get it but I would have thought you are miles short of being able to break even on running costs, even versus bottled gas.

 

[montyjohn]

I'd be amazed if loft insulation alone was enough to make a HP viable for your building.

Obviously every house is different, but on mine Ventilation and External walls make up almost 75% of the heatloss (42% ventilation, 30% external walls).
Ceilings is a mere 12%.
What really surprised me was my single glazed windows being only 9%.

My take from this is ceiling get prioritised because they are easy and cheap to insulate.
Windows also get prioritised as it's easy to market, and decent windows cut down on draughts and this makes up most of the gains. Plenty of anecdotal "evidence" that double glazing makes a game changing difference to how warm a room feels, but I get this is because their old windows were leaking.

So, sealing draughts appears to be the most important improvement you can make.
But it's tricky to sell so doesn't get much publicity.
It also needs to be done in a way where you don't prevent ventilation all together.

 

[montyjohn]

Ideally for an old house you'd be using sheeps wool insulation but its considerably (predictably) more expensive. There's also another breathable product called Thermofloc (recycled paper) which is cheaper with better 'U' value.

Just a correction, whilst Thermofloc has many advantages, it's U value isn't one of them.

Thermofloc - 0.039 W/mK
Wood Fiber Board - 0.039 W/mK
Sheep's Wool - 0.036 W/mK
Rockwool - 0.036 W/mK
Glass - 0.030 W/mK
PIR - 0.022 W/mK

Damn, PIR works well.

 

[anxiouscat]

Thermofloc is great for awkward shaped spaces. Its very dusty so best used where its not likely to be disturbed afterwards.



Depends on how your internal walls are lined. Common construction method in Scotland is to have the plaster stood off the masonry on studs creating a cavity behind. This creates a capillary break in the same way a cavity wall does. If your walls are like that then you should leave the insulation just short of the external walls so that air can still circulate around the cavity and wick away any moisture than penetrates the masonry.

I'd be amazed if loft insulation alone was enough to make a HP viable for your building. Does the installer propose any other improvements? Of course if you don't already have loft insulation then you should absolutely get it but I would have thought you are miles short of being able to break even on running costs, even versus bottled gas.

Thank you, that's interesting to know. The heat loss survey was done a couple of days ago - I haven't seen the results of that yet but assume I will find out more next week, when they are coming to do a technical survey which looks at the specifics of the system in detail.

 

[anxiouscat]

Obviously every house is different, but on mine Ventilation and External walls make up almost 75% of the heatloss (42% ventilation, 30% external walls).
Ceilings is a mere 12%.
What really surprised me was my single glazed windows being only 9%.

My take from this is ceiling get prioritised because they are easy and cheap to insulate.
Windows also get prioritised as it's easy to market, and decent windows cut down on draughts and this makes up most of the gains. Plenty of anecdotal "evidence" that double glazing makes a game changing difference to how warm a room feels, but I get this is because their old windows were leaking.

So, sealing draughts appears to be the most important improvement you can make.
But it's tricky to sell so doesn't get much publicity.
It also needs to be done in a way where you don't prevent ventilation all together.

I can see what you mean, definitely easier to sell loft insulation or double glazing rather than fixing ventilation issues which would be customised to each house and trickier to do. Did you get those heat loss figures for your house from a heat loss survey? My heat loss survey was done a couple of days ago, but I haven't seen results yet (the HP installer is coming out next week to look at all the technical details, so I assume they will have the results with them).

My neighbour just had an extension redone - a really old one that was removed and replaced with newer and slightly bigger. They used PIR in the new roof (not sure if they put it in the rest of her loft though, I'll ask her).

 

[paulc]

My take from this is ceiling get prioritised because they are easy and cheap to insulate.
Windows also get prioritised as it's easy to market, and decent windows cut down on draughts and this makes up most of the gains. Plenty of anecdotal "evidence" that double glazing makes a game changing difference to how warm a room feels, but I get this is because their old windows were leaking.

Loft insulation is indeed both a cheap and an easy fix - Got between 300mm and 400mm in mine, slightly less where the roof meets the walls..
Windows were well worth doing as the old (1970s) ones were badly fitted, sealed units blown, and cold draughts coming in. With the new windows, I benefit from a noticeable solar gain during the winter months when the sun is shining. When the sun is out, the extra gain often often means that the heating doesn't kick in during the daytime. However, it is unlikely that I'll recover the cost of new windows from savings on heating in my lifetime. But it has made a huge difference in quality of life which one can't put a value on.

 

[anxiouscat]

But it has made a huge difference in quality of life which one can't put a value on.

Absolutely, well said.

The previous owners of my house did a lot of work to it, including changing the single glazed windows for double glazing. On the whole, my house is actually already nice and warm, despite not having things like loft insulation, and bills are pretty much on a par with my previous house which was a lot newer (1978 vs 1850), roughly the same size, and had loft insulation. That said, if loft insulation can make my bills decrease even further, then that's a happy bonus!

 

[mh12]

Obviously every house is different, but on mine Ventilation and External walls make up almost 75% of the heatloss (42% ventilation, 30% external walls).
Ceilings is a mere 12%.
What really surprised me was my single glazed windows being only 9%.

Mighty interesting set of figures. I don't have the exact figures to hand but was under the impression the most of the heat loss occurs through un insulated roof space and walls.

Suspect you've probably maxed out on roof insulation hence low heat loss compared to walls.

The figure quoted of heat loss via ventilation is that due to disused uncapped chimney's where the disused fireplace opening hasn't been blocked with some sort of insulation?