New Build Insulation Conundrum

SelfBuild21 · 12-01-2021 10:16pm #1

Hi all, we are doing a new build and our engineer has speced partial fill insulation in the cavity (110 xtrowall plus no internal dry lining). We hear so many opinions about all the diff types of insulation and were looking for experience from people who have this spec and are now living in the house, and wondering how they find it? Any regrets etc Thanks in advance for any help

BryanF · 12-01-2021 11:57pm

Hi welcome

What stage are you at exactly? Tenders returned?

Drylining is not really the way to go. Research ‘thermal mass’.

Gumbo · 13-01-2021 12:48am

I don’t think I could build new without going EWI, UFH and A2W at this point in time.

Calahonda52 · 13-01-2021 9:55am

Its not all about insulation , airtightness comes first and you need to get a ACH target put in place with your engineer and builder, now, at the design stage.
if you do a full LCCA, allowing for carbon tax increases on energy+ fuel cost increases over say 30 years you need to be doing what Gumbo suggests ++
The additional cost of getting to both A+ at this point plus great comfort, is maybe 10%, so reduce the footprint enough to still keep on budget.
The MHVR needs to be designed now, not as an afterthought.

Look at the Green Building Store and Enhabit websites, some details recently on how to hang windows on the outside of the outer with EWI to eliminate thermal bridges.

SelfBuild21 · 13-01-2021 10:42am

Hi guys, thanks for the replies. At the moment we are out to tenders with a few contractors, hoping they come back within budget , or else it will be direct labour for us

As I mentioned the engineer has specd partial fill cavity, no internal dry lining. His thinking behind this, is that the dry lining prevents the inner block acting like a thermal mass. Makes sense to me, but just a bit worried because we see so many other options and wondering how this works in theory?

We have A2W, UFH, MHR , will use air tightness membrane on the ceilings and around doors/windows to seal against the blockwork. Getting a provisional BER of A2

Gumbo · 13-01-2021 11:20am

SelfBuild21 wrote: »

Hi guys, thanks for the replies. At the moment we are out to tenders with a few contractors, hoping they come back within budget , or else it will be direct labour for us

As I mentioned the engineer has specd partial fill cavity, no internal dry lining. His thinking behind this, is that the dry lining prevents the inner block acting like a thermal mass. Makes sense to me, but just a bit worried because we see so many other options and wondering how this works in theory?

We have A2W, UFH, MHR , will use air tightness membrane on the ceilings and around doors/windows to seal against the blockwork. Getting a provisional BER of A2

Your meeting minimum regulations. That’s all. Don’t be fooled Into thinking your going super.

You should be aiming higher than the minimum regulations in my
Opinion. You only get one change to do it.

GreeBo · 13-01-2021 11:24am

SelfBuild21 wrote: »

Hi guys, thanks for the replies. At the moment we are out to tenders with a few contractors, hoping they come back within budget , or else it will be direct labour for us

As I mentioned the engineer has specd partial fill cavity, no internal dry lining. His thinking behind this, is that the dry lining prevents the inner block acting like a thermal mass. Makes sense to me, but just a bit worried because we see so many other options and wondering how this works in theory?

We have A2W, UFH, MHR , will use air tightness membrane on the ceilings and around doors/windows to seal against the blockwork. Getting a provisional BER of A2

Why would you want to prevent the walls acting as a thermal mass?

TheBoyConor · 13-01-2021 11:35am

Depending on the use of a building, you might want to have or avoid thermal mass. Somewhere that is continuously occupied, like a nursing home, hotel, garda station etc, you would want the thermal mass as a buffer against big or fast thermal swings. However, thermal mass takes a long time to heat up in the beginning. So somewhere that only has intermittent occupation would be better off with less thermal mass so that they heat up quicker and not all the stored heat ends up wasted when people leave the building. Places like student accommodation, some offices, schools, houses of single people or couples who are out at work all day and out most evenings etc would fall into this category.
A house falls somewhere in between depending on the occupancy pattern. A family home where the mother is the full time care giver at home will have more benefit of thermal mass, but a rented house of a working couple or a single person who is out at work all day, would probably benefit more from low thermal mass so it heats up quickly when you arrive home. If you had too much thermal mass it would only be fully heated up by the time you'd be ready to go out the door again.
The problem with that approach is that occupancy patterns could and would change over the years. So what do you do? Do you make your best guess at what type of lifestyle or occupancy pattern the future will bring and build accordingly?

It only makes sense to aim above the minimum standard if you are going to live in the house yourself. If building houses for sale, or for rent, well the new owners or tenant will be paying the heating bills, so there will be little to no return on investment for building in excess of the minimum standards.

SelfBuild21 · 13-01-2021 12:05pm

Gumbo wrote: »

Your meeting minimum regulations. That’s all. Don’t be fooled Into thinking your going super.

You should be aiming higher than the minimum regulations in my
Opinion. You only get one change to do it.

O wow, didnt know A2 was only the minimum standard. Can you tell me what you recommend then? With regards to insulation , blockwork, product/model type etc. Thanks in advance

Tefral · 13-01-2021 12:10pm

SelfBuild21 wrote: »

O wow, didnt know A2 was only the minimum standard. Can you tell me what you recommend then? With regards to insulation , blockwork, product/model type etc. Thanks in advance

to confuse you further, dont just be relying on your BER result.

Always keep your insulation in one place. There's no need to be insulating slabbing the internal walls of a house in a new build. Increase the cavity and keep all the insulation within that.

TheBoyConor · 13-01-2021 12:12pm

Exactly. Slabbing the inside of a new house doesn't sit well with me at all. It just seems like it'll be extra expensive and no real advantage over a wider cavity. And less robust against damage.

GreeBo · 13-01-2021 12:12pm

TheBoyConor wrote: »

If you had too much thermal mass it would only be fully heated up by the time you'd be ready to go out the door again.

But once its heated thats pretty much it, when you come home the its still warm?

There is an initial slow ramp up, but once its up to temp it takes very little to keep it there, isnt that the whole point?

Now if its a summer holiday home type of thing that will be empty 6 months of the year it might not make sense, but for any primary dwelling it only makes sense (to me!) to utilise the thermal mass.

Tefral · 13-01-2021 12:16pm

TheBoyConor wrote: »

Exactly. Slabbing the inside of a new house doesn't sit well with me at all. It just seems like it'll be extra expensive and no real advantage over a wider cavity. And less robust against damage.

Yep adds alot of cost, and its a nightmare to fix anything heavy afterward in terms of using bigger fixings for it.

the more surfaces you have with different temperatures etc the greater the chances of issues with dew points etc.

SelfBuild21 · 13-01-2021 12:19pm

Tefral wrote: »

to confuse you further, dont just be relying on your BER result.

Always keep your insulation in one place. There's no need to be insulating slabbing the internal walls of a house in a new build. Increase the cavity and keep all the insulation within that.

Ok thanks. Yes completely agree, the BER result is only in theory. Do you think full fill or partial fill cavity is better?

Calahonda52 · 13-01-2021 12:21pm

SelfBuild21 wrote: »

O wow, didnt know A2 was only the minimum standard. Can you tell me what you recommend then? With regards to insulation , blockwork, product/model type etc. Thanks in advance

In fairness, don't expect a free design class here.:D
The BER is a distraction, you need to take to your engineer about what it will take to get to Passiv or close thereto.
Did the tenders specify a target ACH?
A2 is a wasted opportunity, tough to get with direct labour anyway.
As I said, price it up for near Passiv and reduce the footprint to suit

Tefral · 13-01-2021 12:24pm

SelfBuild21 wrote: »

Ok thanks. Yes completely agree, the BER result is only in theory. Do you think full fill or partial fill cavity is better?

Personally with the weather we have here and driving rain etc. I always prescribed to the idea of leaving a gap between the front wall of the cavity and the insulation. That's just personal opinion and there's a lot of evidence out there to suggest it isn't an issue. So in my opinion id be making the cavity bigger to accommodate the best U-Value you can get in the cavity and still maintaining a gap.

There are issues with making a cavity too wide with regards to wall ties etc so its best speaking with your engineer.

Good attention to detail on thermal bridging at the slab level with thermal blocks and airtightness are just as important.

TheBoyConor · 13-01-2021 12:49pm

GreeBo wrote: »

But once its heated thats pretty much it, when you come home the its still warm?

There is an initial slow ramp up, but once its up to temp it takes very little to keep it there, isnt that the whole point?

Now if its a summer holiday home type of thing that will be empty 6 months of the year it might not make sense, but for any primary dwelling it only makes sense (to me!) to utilise the thermal mass.

I would look at it differently. If you are out working all day, and perhaps gone out an our or 2 most evenings, you are then in a situation where the house is effectively heated 24/7 due to the attenuating effect of the TM. Sure, the heating appliance might only on for 8 or 12 hours, but in those hours it has to put back in the energy deficit lost from the thermal mass over the other 12 or 16 hours. So the net result is the house is effectively heated all the time.
That means there is a significant cost attached. heating a house which is unoccupied most of the time.

Under normal circumstances, I'd be out of the house no later than 7. Perhaps home at 6, Dinner. Then I could be gone out for another 2 or 3 hours at various things, then be home about 9 or 10 and into bed. In my situation a low thermal mass would suit. Let the house cool down when I'm not home, which is a lot of the time, and when I come home have it set to heat up quickly. Only have heat in the house when I am there to make use of it.
That seems the most logical approach to me. No point having a warm house if there is no-one in the house to feel the warmth.

Tefral · 13-01-2021 12:50pm

TheBoyConor wrote: »

I would look at it differently. If you are out working all day, and perhaps gone out an our or 2 most evenings, you are then in a situation where the house is effectively heated 24/7 due to the attenuating effect of the TM. Sure, the heating appliance might only on for 8 or 12 hours, but in those hours it has to put back in the energy deficit lost from the thermal mass over the other 12 or 16 hours. So the net result is the house is effectively heated all the time.
That means there is a significant cost attached. heating a house which is unoccupied most of the time.

Under normal circumstances, I'd be out of the house no later than 7. Perhaps home at 6, Dinner. Then I could be gone out for another 2 or 3 hours at various things, then be home about 9 or 10 and into bed. In my situation a low thermal mass would suit. Let the house cool down when I'm not home, which is a lot of the time, and when I come home have it set to heat up quickly. Only have heat in the house when I am there to make use of it.
That seems the most logical approach to me. No point having a warm house if there is no-one in the house to feel the warmth.

except that isnt the case if you have a heatpump. your stats are set to 20/21 degrees and your pump just keeps it at that level whether you are there or not.

SelfBuild21 · 13-01-2021 12:51pm

Tefral wrote: »

Personally with the weather we have here and driving rain etc. I always prescribed to the idea of leaving a gap between the front wall of the cavity and the insulation. That's just personal opinion and there's a lot of evidence out there to suggest it isn't an issue. So in my opinion id be making the cavity bigger to accommodate the best U-Value you can get in the cavity and still maintaining a gap.

There are issues with making a cavity too wide with regards to wall ties etc so its best speaking with your engineer.

Good attention to detail on thermal bridging at the slab level with thermal blocks and airtightness are just as important.

Ok cheers for that. From the research Ive done I agree with leaving a gap in the cavity. I suppose after that, it all comes down to finding the sweet spot for the cavity gap/insulation thickness and what U values etc you are trying to achieve. Thanks for the advice, appreciated 👍👍

TheBoyConor · 13-01-2021 12:56pm

Tefral wrote: »

except that isnt the case if you have a heatpump. your stats are set to 20/21 degrees and your pump just keeps it at that level whether you are there or not.

In that case, perhaps a heat pump is not the most appropriate for a place with intermittent occupancy? Like it may be very efficient and all, but if there is no-one in the house to use the heat, then is it not just effectively wasted, no matter how efficient the system might be from a technical point of view.

Can an A2A heat pump not cycle on/off in response to when a demand is placed by a timer?

GreeBo · 13-01-2021 12:57pm

TheBoyConor wrote: »

I would look at it differently. If you are out working all day, and perhaps gone out an our or 2 most evenings, you are then in a situation where the house is effectively heated 24/7 due to the attenuating effect of the TM. Sure, the heating appliance might only on for 8 or 12 hours, but in those hours it has to put back in the energy deficit lost from the thermal mass over the other 12 or 16 hours. So the net result is the house is effectively heated all the time.
That means there is a significant cost attached. heating a house which is unoccupied most of the time.

Under normal circumstances, I'd be out of the house no later than 7. Perhaps home at 6, Dinner. Then I could be gone out for another 2 or 3 hours at various things, then be home about 9 or 10 and into bed. In my situation a low thermal mass would suit. Let the house cool down when I'm not home, which is a lot of the time, and when I come home have it set to heat up quickly. Only have heat in the house when I am there to make use of it.
That seems the most logical approach to me. No point having a warm house if there is no-one in the house to feel the warmth.

Hang on, how much heat is being "lost from the thermal mass"?
The house is going to be insulated, we aren't talking about some 9in cavities sitting in a field!

The A2W is going to be running anyway, regardless of you being there, so the house is always at whatever temp you have it set to.
You seem to be planning on having a low thermal mass and having the gas boiler timed to come on when you are in the house? I'd say thats very 1980's thinking...

You are also ignoring the fact that your house will lose the heat very quickly, so when the front door is open paying the milkman, all your hot air is escaping, and since you don't have any thermal mass, all your energy went into heating the air (which has now escaped)

GreeBo · 13-01-2021 12:58pm

TheBoyConor wrote: »

In that case, perhaps a heat pump is not the most appropriate for a place with intermittent occupancy?

Can an A2A heat pump not cycle on/off in response to when a demand is placed by a timer?

Thats not how they work though, a heat pump isnt going to be able to provide enough heat on demand, it works by consistently and constantly adding a small amount of energy to the building, the thermal mass holds onto the energy and so your house is always comfortable.

A HP is going to be giving you temps of ~22* on yoru rads/UFH, its not designed to replace a gas boiler throwing out 75*

TheBoyConor · 13-01-2021 1:05pm

Ah ok. I understand now. Thanks

As such I am assuming that a heat pump is therefore more suited towards situations that call for a constant heat level. Intermittently occupied properties would be more geared to something like a boiler that can provide a lot of heat in a short space of time.

My point still stands though, if a dwelling is only intermittently occupied, as mine normally would be, it would be more efficient in an overall cost at the end of the year sense, to only heat it for those times of the day when you are actually in the house. And a low thermal mass suits that scenario better.

sydthebeat · 13-01-2021 1:05pm

TheBoyConor wrote: »

In that case, perhaps a heat pump is not the most appropriate for a place with intermittent occupancy? Like it may be very efficient and all, but if there is no-one in the house to use the heat, then is it not just effectively wasted, no matter how efficient the system might be from a technical point of view.

Can an A2A heat pump not cycle on/off in response to when a demand is placed by a timer?

You can't design a house for intermittent occupancy, especially a family home.

An apartment, maybe, but not a family home. First principles would have to assume full time occupancy at some stage during the buildings existence, and you must design to that.

TheBoyConor · 13-01-2021 1:15pm

Yes I understand that. And that is a family home, which has a much greater probability of a high % occupancy.
And I know there are certain criteria that you must assume. Minimum standards that must be observed regardless of the situation. But that doesn't mean that they are always accurate or that real-life conditions reflect those assumtions.

For example. My house is likely a BER D or E, at best. An assessor would advise me to insulate, upgrade windows, this that etc, deep retrofit at very significant cost and I'd possibly save X amount of energy and €s per year. Except that wouldn't be reflected in reality. It is only myself here, I am gone most of the day and I spend a relatively modest amount on heating the house as I only fully heat the rooms that I use at the times that i'd be using them. Much less than if I had a family of 4 here. To do a deep retrofit here would be false economy and throwing money away, because while it may all sound and look very well on paper according to assumptions, in reality it would simply never pay for itself. So, even as someone who has a fairly good understanding of this field, having worked as an engineer in a county Energy Agency, I would never be too inclined to do any significant energy upgrades on my house, because I know the numbers don't stack up for me when the actual real world use conditions are accounted for.

I once looked at the idea of installing PV. But then on delving into it, I dont really use that much electricity at all anyway, so by the time a PV system had paid for itself, it would be probably already crocked and in need of replacement. So it simply made no sense to do it.

JimmyMW · 13-01-2021 1:17pm

TheBoyConor wrote: »

I would look at it differently. If you are out working all day, and perhaps gone out an our or 2 most evenings, you are then in a situation where the house is effectively heated 24/7 due to the attenuating effect of the TM. Sure, the heating appliance might only on for 8 or 12 hours, but in those hours it has to put back in the energy deficit lost from the thermal mass over the other 12 or 16 hours. So the net result is the house is effectively heated all the time.
That means there is a significant cost attached. heating a house which is unoccupied most of the time.

Under normal circumstances, I'd be out of the house no later than 7. Perhaps home at 6, Dinner. Then I could be gone out for another 2 or 3 hours at various things, then be home about 9 or 10 and into bed. In my situation a low thermal mass would suit. Let the house cool down when I'm not home, which is a lot of the time, and when I come home have it set to heat up quickly. Only have heat in the house when I am there to make use of it.
That seems the most logical approach to me. No point having a warm house if there is no-one in the house to feel the warmth.

My house is 2000sq Ft with a heat pump, house is always warm with ample hot water on demand, yearly costs approx <€600/year to run, its a very cheap system to run when combined with MVHR and a well detailed/Insulated/Airtight house. Also to note i am out of the house for 12 hours a day min, i am the only occupant

GreeBo · 13-01-2021 1:29pm

TheBoyConor wrote: »

Ah ok. I understand now. Thanks

As such I am assuming that a heat pump is therefore more suited towards situations that call for a constant heat level. Intermittently occupied properties would be more geared to something like a boiler that can provide a lot of heat in a short space of time.

My point still stands though, if a dwelling is only intermittently occupied, as mine normally would be, it would be more efficient in an overall cost at the end of the year sense, to only heat it for those times of the day when you are actually in the house. And a low thermal mass suits that scenario better.

I wouldn't call a few hours every day "intermittent" though, I guess that's the difference.

In a well insulated, "airtight" house a high thermal mass and HP will mean that your house will stay very warm for very little energy while you are out and be cosy anytime you are in it.

Your running costs for the intermittent (but everyday) high output boiler will be higher than the slow'n'low constant output of a HP with high thermal mass.

GreeBo · 13-01-2021 1:30pm

TheBoyConor wrote: »

Yes I understand that. And that is a family home, which has a much greater probability of a high % occupancy.
And I know there are certain criteria that you must assume. Minimum standards that must be observed regardless of the situation. But that doesn't mean that they are always accurate or that real-life conditions reflect those assumtions.

For example. My house is likely a BER D or E, at best. An assessor would advise me to insulate, upgrade windows, this that etc, deep retrofit at very significant cost and I'd possibly save X amount of energy and €s per year. Except that wouldn't be reflected in reality. It is only myself here, I am gone most of the day and I spend a relatively modest amount on heating the house as I only fully heat the rooms that I use at the times that i'd be using them. Much less than if I had a family of 4 here. To do a deep retrofit here would be false economy and throwing money away, because while it may all sound and look very well on paper according to assumptions, in reality it would simply never pay for itself. So, even as someone who has a fairly good understanding of this field, having worked as an engineer in a county Energy Agency, I would never be too inclined to do any significant energy upgrades on my house, because I know the numbers don't stack up for me when the actual real world use conditions are accounted for.

I once looked at the idea of installing PV. But then on delving into it, I dont really use that much electricity at all anyway, so by the time a PV system had paid for itself, it would be probably already crocked and in need of replacement. So it simply made no sense to do it.

Ah, you are talking about an old house retrofit whereas we are all talking about a new build for the OP...

Calahonda52 · 13-01-2021 1:53pm

SelfBuild21 wrote: »

Ok cheers for that. From the research Ive done I agree with leaving a gap in the cavity. I suppose after that, it all comes down to finding the sweet spot for the cavity gap/insulation thickness and what U values etc you are trying to achieve. Thanks for the advice, appreciated 👍👍

Leaving a gap in an insulated cavity works really, really well ...... in CAD

As for achieving it on a wet and windy site with

piss poor scaffolding
poorly stored material
blunt cutting gear
and a hangover

and getting it fitted tight fitting at joins etc, with no gaps, well, is the stuff Lewis Carroll wrote about in Alice and Wonderland

BryanF · 13-01-2021 2:02pm

TheBoyConor wrote: »

Depending on the use of a building, you might want to have or avoid thermal mass. Somewhere that is continuously occupied, like a nursing home, hotel, garda station etc, you would want the thermal mass as a buffer against big or fast thermal swings. However, thermal mass takes a long time to heat up in the beginning. So somewhere that only has intermittent occupation would be better off with less thermal mass so that they heat up quicker and not all the stored heat ends up wasted when people leave the building. Places like student accommodation, some offices, schools, houses of single people or couples who are out at work all day and out most evenings etc would fall into this category.
A house falls somewhere in between depending on the occupancy pattern. A family home where the mother is the full time care giver at home will have more benefit of thermal mass, but a rented house of a working couple or a single person who is out at work all day, would probably benefit more from low thermal mass so it heats up quickly when you arrive home. If you had too much thermal mass it would only be fully heated up by the time you'd be ready to go out the door again.
The problem with that approach is that occupancy patterns could and would change over the years. So what do you do? Do you make your best guess at what type of lifestyle or occupancy pattern the future will bring and build accordingly?

It only makes sense to aim above the minimum standard if you are going to live in the house yourself. If building houses for sale, or for rent, well the new owners or tenant will be paying the heating bills, so there will be little to no return on investment for building in excess of the minimum standards.

I have to disagree with pretty much everything above.
Modern heating systems should run at low level, continuously. Good building fabric Should not heat up/ cool down in 24 hour period, the above post is out of date with current thinking off heat pumps etc.

And as for ‘return on investment‘, I’d like to think a house I’d design/build for a Tennent should be constructed as well as a house I’d build for my self.

TheBoyConor · 13-01-2021 2:22pm

Calahonda52 wrote: »

Leaving a gap in an insulated cavity works really, really well ...... in CAD

As for achieving it on a wet and windy site with
piss poor scaffolding

poorly stored material

blunt cutting gear

and a hangover

and getting it fitted tight fitting at joins etc, with no gaps, well, is the stuff Lewis Carroll wrote about in Alice and Wonderland

100%.

All of the above not to mention the fact that a wall cavity is out of sight and therefore out of mind. You'll be going well if half of the insulation makes it into the wall cavity at all once no-body in authority is watching, not to mind there being no gaps or pressed tight against the inner leaf.

I have seen walls insulated with badly cut, or cut wrong pieces of insulation, insulation fúcked in any old way sure who cares if there's gaps or broken sheets - no-one's gonna see it anyway. or in one case they just decided to stop installing insulation half way up a gable wall because they ran out, but carried on with the blocks anyway and slipped one row of sheets in along from the top of the gable so it looked right at a glance.

I've also seen insulation omitted and all the plastic wrapping, block bale straps and other site rubbish stuffed down into the cavity in lieu of insulation because the contractor was too tight to pay for a skip and had already been told off for burning stuff. Again, topped of with a row of sheets to hide it, expecting that a check would be no more than a quick passing glance at it.

Add in to the equation the dreaded apprentice (once it is in the wall it's ok right? Tight again the block? the outer blocks right? sure that's where the cold is, no?

And the above wasn't from random cowboy man-in-van outfits either. This was contractors who, on the face of it, looked like a reputable quality above board business, ISO quality and safety certifications, fancy website, slick social media videos of their projects, 100 or more staff on different projects.

Unless you stand over most of these fellas you'd end up with a build any celtic tiger suckler farmer turned property tycoon would be proud of. Especially for elements that are not outwardly visible on the finished house.

New Build Insulation Conundrum

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