Drylining and Wall Insulation

kerrypod

Hi, I'm building a new two storey house and am looking for some advice on the insulation side of things for the cavity walls.
The drawings from the engineer specify a 100mm external leaf, 150mm cavity fully filled with Pumped Bead insulation, a 100mm inner leaf and 50mm insulated plasterboard fixed to inside using dot/dab plaster.
We are not using Mechanical Heat Recovery Ventilation, we are just using natural wall vents throughout the house.
I've read on a number of threads that drylining is not recommended for new houses in Ireland if possible due to the risk of condensation, damp and mould.
Are there any builders/engineers that may have experience of this type of wall construction? Could you advise on whether I am asking for trouble going with this system? Or should it be ok considering there is a cavity wall being used?
Thanks

Rabbo

Firstly, it's madness not installing a mechanical heat recovery ventilation system in a new house.
To comply with current building regulations, you will need to go to significant expense and trouble to achieve reasonable airtightness level in the house. To then go and poke a series of 100mm vent holes in the wall is crazy. An MHRV system (or equivalent) is a critical part of a modern well insulated, airtight and adequately ventilated house.

To minimise the risk of interstitial condensation at least two thirds of your wall insulation should be located in the cavity. Given that the drylining would be high denisty PU insulation, i.e. a better insulator than the equivalent thickness of bead, your proposed wall construction may have an risk of interstitial condensation issues. There also other factors to consider like loss of thermal mass, difficulty in achieving continuity of the drylining (i.e. through floor joists, internal wall, etc) and difficulty with fixing to the walls afterwards, I'd steer away from drylining in a new house. There are full-fill high density PU cavity insulation products available that can achieve a respectable u value of 0.15 within a 150mm cavity. Any cavities greater than 150mm require special structural design from a structural engineer.

kerrypod

Rabbo wrote: »

Firstly, it's madness not installing a mechanical heat recovery ventilation system in a new house.
To comply with current building regulations, you will need to go to significant expense and trouble to achieve reasonable airtightness level in the house. To then go and poke a series of 100mm vent holes in the wall is crazy. An MHRV system (or equivalent) is a critical part of a modern well insulated, airtight and adequately ventilated house.

I suppose my main problem is the budget. I will be using solar panels anyway, and buying a MHRV system would be another major dent in my funds. I have about 150k to build a 250sqm two storey house. Achieving a high energy rating isn't too important as I never intend to sell the house. However, I don't want to make any drastically bad errors in construction which could cause me problems down the line. If natural vents are ok to use under Building Regs I will have to use them I'm afraid.

893bet

kerrypod wrote: »

I suppose my main problem is the budget. I will be using solar panels anyway, and buying a MHRV system would be another major dent in my funds. I have about 150k to build a 250sqm two storey house. Achieving a high energy rating isn't too important as I never intend to sell the house. However, I don't want to make any drastically bad errors in construction which could cause me problems down the line. If natural vents are ok to use under Building Regs I will have to use them I'm afraid.

At that budget the build is no where near possible!

A high energy rated house is not an optional undertaking. It is enshrined in the building regulations. Don't see it as a negative thing, only useful if you want to sell. Given you plan on never selling and always living in the house then you want it to be cheaper to run long term and comfortable? I think you need to adjust your perspective or you may regret it in 10 years time. What use is spending a fortune on insulayion and then punching holes in the wall for all your heat to pour out?

Have you planning already gotten? If not I would look to scale back your plans to suit your budget.

kerrypod

Yes, planning received and started on site with a couple of weeks. I'm up to finished floor level at the moment, so I won't be scaling back on the floor area. What I might end up doing is leaving 2 out of 4 of the upstairs bedrooms incomplete. But I'm ok with that as long as the main living areas are habitable.

A lot of the build will be self build so I should get it done eventually!

893bet

kerrypod wrote: »

Yes, planning received and started on site with a couple of weeks. I'm up to finished floor level at the moment, so I won't be scaling back on the floor area. What I might end up doing is leaving 2 out of 4 of the upstairs bedrooms incomplete. But I'm ok with that as long as the main living areas are habitable.

A lot of the build will be self build so I should get it done eventually!

Have you a Assigned certifer on board that is happy with the self build aspect ?

On your budget I can't see you getting it done. Not unless it is substandard and cheap finish and no where even near regulations.

kerrypod

Ya there nothing strictly speaking in the BCM Regs to stop self builds as long as the assigned certifier is happy to sign off on the works.
In fact the builder doesn't even have to be registered - it is only recommended by the BCM Regs.

893bet

kerrypod wrote: »

Ya there nothing strictly speaking in the BCM Regs to stop self builds as long as the assigned certifier is happy to sign off on the works.
In fact the builder doesn't even have to be registered - it is only recommended by the BCM Regs.

I don't know so can't comment but of you have your AC on board then fair enough.

Either way with your budget you won't be able to meet building regulation so the AC shouldnt be signing off. Maybe he will eitherway. You will be left with a substandard home for your investment.

I don't think anyone is going to change your mind though so good luck with it.

kerrypod

Rabbo wrote: »

To minimise the risk of interstitial condensation at least two thirds of your wall insulation should be located in the cavity. Given that the drylining would be high denisty PU insulation, i.e. a better insulator than the equivalent thickness of bead, your proposed wall construction may have an risk of interstitial condensation issues. There also other factors to consider like loss of thermal mass, difficulty in achieving continuity of the drylining (i.e. through floor joists, internal wall, etc) and difficulty with fixing to the walls afterwards, I'd steer away from drylining in a new house. There are full-fill high density PU cavity insulation products available that can achieve a respectable u value of 0.15 within a 150mm cavity. Any cavities greater than 150mm require special structural design from a structural engineer.

Well to be honest, the U-value of the 150mm Ecobead insulation is working out at 0.22 using a thermal conductivity of 0.033. If I used the 37.5mm insulation on inside with conductivity of 0.026, the U-value is 0.6933 so I should be ok as regards condensation right?

Gumbo

kerrypod wrote: »

Ya there nothing strictly speaking in the BCM Regs to stop self builds as long as the assigned certifier is happy to sign off on the works.
In fact the builder doesn't even have to be registered - it is only recommended by the BCM Regs.

What does your preliminary BER Report say?
Try changing everything digitally first and then build.

Personally speaking, i think its foolish to be at this stage of the build and not have your details ironed out, especially something as important as the Part L compliance, its very hard to correct if you go to far!

Calahonda52

kerrypod wrote: »

....and 50mm insulated plasterboard fixed to inside using dot/dab plaster.

Others have given you goo advice which seems to be perhaps unwelcome so hopefully this will not get too harsh a response.

Dot/ dab on plain concrete block walls is a rubbish construction for a variety of reasons.
The one I want to focus on here is that the blockwork is very porous and will be a continuous way to lose heat, behind the board which is much reduced in effectiveness.

How is the design catering for services such as wiring behind the board?

What width of insulation is on the window doors reveals?

Are the internal walls dry lined as well?

BryanF

kerrypod wrote: »

Well to be honest, the U-value of the 150mm Ecobead insulation is working out at 0.22 using a thermal conductivity of 0.033. If I used the 37.5mm insulation on inside with conductivity of 0.026, the U-value is 0.6933 so I should be ok as regards condensation right?

Incorrect.

In your first post you state you don't know much about insulation. Are you competent to be the main contractor? Under the new BC regs you sign as being a competent builder..

murphy31ie

Rabbo wrote: »

Firstly, it's madness not installing a mechanical heat recovery ventilation system in a new house.
To comply with current building regulations, you will need to go to significant expense and trouble to achieve reasonable airtightness level in the house. To then go and poke a series of 100mm vent holes in the wall is crazy. An MHRV system (or equivalent) is a critical part of a modern well insulated, airtight and adequately ventilated house.

To minimise the risk of interstitial condensation at least two thirds of your wall insulation should be located in the cavity. Given that the drylining would be high denisty PU insulation, i.e. a better insulator than the equivalent thickness of bead, your proposed wall construction may have an risk of interstitial condensation issues. There also other factors to consider like loss of thermal mass, difficulty in achieving continuity of the drylining (i.e. through floor joists, internal wall, etc) and difficulty with fixing to the walls afterwards, I'd steer away from drylining in a new house. There are full-fill high density PU cavity insulation products available that can achieve a respectable u value of 0.15 within a 150mm cavity. Any cavities greater than 150mm require special structural design from a structural engineer.

Sorry to jump on this, are you saying there is a high risk of condensation if you have 150mm full cavity and 50 plasterboard.?

kerrypod

Calahonda52 wrote: »

Others have given you goo advice which seems to be perhaps unwelcome so hopefully this will not get too harsh a response.

Dot/ dab on plain concrete block walls is a rubbish construction for a variety of reasons.
The one I want to focus on here is that the blockwork is very porous and will be a continuous way to lose heat, behind the board which is much reduced in effectiveness.

How is the design catering for services such as wiring behind the board?

What width of insulation is on the window doors reveals?

Are the internal walls dry lined as well?

ah no im welcoming all the advice but the budget for the build is tight and a lot of this is contradicting the advice my engineer gave me so im a bit worried! The insulation around doors windows will be reduced to 25mm. Do you think mechanically fixed would be a better option? Should i have the walls sand/cement plastered before i fix the insulated plasterboard to it? I didnt intend doing internal walls with insulated plasterboard no... Is this an issue? I presume its ok to still chase the block wall and bring the wires out through drylining boxes?

kerrypod

BryanF wrote: »

Incorrect.

In your first post you state you don't know much about insulation. Are you competent to be the main contractor? Under the new BC regs you sign as being a competent builder..

hi could you explain why thats incorrect thanks

kerrypod

kceire wrote: »

What does your preliminary BER Report say?
Try changing everything digitally first and then build.

Personally speaking, i think its foolish to be at this stage of the build and not have your details ironed out, especially something as important as the Part L compliance, its very hard to correct if you go to far!

Ya all the details i mentioned have been designed into the BER report by the engineer and im getting an A2 rating..... Its just the risk of damp/mould that is freaking me out!

893bet

kerrypod wrote: »

Ya all the details i mentioned have been designed into the BER report by the engineer and im getting an A2 rating..... Its just the risk of damp/mould that is freaking me out!

There is zero chance you can take a 2500 sq foot build to anywhere near A rated with 150k unless you mean a very basic builders finish.

Your first few posts mention that you don't care about energy rating yet now have a spec for an A2 house?

BryanF

kerrypod wrote: »

hi could you explain why thats incorrect thanks

Hi it's my day off, so someone else can do your sums for you, but the 150 cavity & 50mm drylining is hardly Reaching a wall u-value of 0.69 wm2k and condensation risk is likely anywhere your thermal bridge detailing is poor for example window reveals - my advise keep all the insulation in one zone. As for air-tightness - forget the drylining and plaster the walls with specialist air-tightness tape at all junctions including plastering chases and backboxes. Do the ber assessment now and consider doing an air-tightness course and passive house course - at least you will have some idea what your doing by the end of them.

Best of luck with your build - 150k for a 250m2 build will not finish the house- you should check with your engineer what exactly s/he considers 'practically complete' for final mortgage/ building regs & planning regs perspectives.

As for competency to build and sign off as the main contractor, you know my view on this.

Calahonda52

OP: read this
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx
and then ask ur engineer to read it and tell u he has met or exceeded all the requirements

sydthebeat

893bet wrote: »

There is zero chance you can take a 2500 sq foot build to anywhere near A rated with 150k unless you mean a very basic builders finish.

Your first few posts mention that you don't care about energy rating yet now have a spec for an A2 house?

From what I've discovered with 2011 part l deap assessments, when you don't use mhrv you actually have to increase the elemental u values so much that you have to hit A2 to meet min regs rather than usual A3.

So it's a real false economy choosing not to use mhrv.

The increased costs of Windows alone would cover the mhrv in most cases.

kerrypod

BryanF wrote: »

Hi it's my day off, so someone else can do your sums for you, but the 150 cavity & 50mm drylining is hardly Reaching a wall u-value of 0.69 wm2k and condensation risk is likely anywhere your thermal bridge detailing is poor for example window reveals - my advise keep all the insulation in one zone. As for air-tightness - forget the drylining and plaster the walls with specialist air-tightness tape at all junctions including plastering chases and backboxes. Do the ber assessment now and consider doing an air-tightness course and passive house course - at least you will have some idea what your doing by the end of them.

Best of luck with your build - 150k for a 250m2 build will not finish the house- you should check with your engineer what exactly s/he considers 'practically complete' for final mortgage/ building regs & planning regs perspectives.

As for competency to build and sign off as the main contractor, you know my view on this.

No need to be a prick about it Im just looking for some advice! Its my house and if i want to invest my own time in building the property where i plan on spending the rest of my days thats my decision to make! I may not be a competent builder like yourself right now but im willing to learn and thats where most idiots fall down!

kerrypod

893bet wrote: »

There is zero chance you can take a 2500 sq foot build to anywhere near A rated with 150k unless you mean a very basic builders finish.

Your first few posts mention that you don't care about energy rating yet now have a spec for an A2 house?

Ya to a certain extent i just want to have a house that meets building regs first and foremost, but from what im reading that means getting a high energy rating anyway! In summary, it sounds like im attempting to build the first ever 250sqm house with an A2 rating for under 150k! God help me!

murphy31ie

kerrypod wrote: »

Ya to a certain extent i just want to have a house that meets building regs first and foremost, but from what im reading that means getting a high energy rating anyway! In summary, it sounds like im attempting to build the first ever 250sqm house with an A2 rating for under 150k! God help me!

I am at second fix stage on a 2500 sq ft house and like every man else trying to keep costs down. Looking like k

893bet

murphy31ie wrote: »

I am at second fix stage on a 2500 sq ft house and like every man else trying to keep costs down. Looking like k

How much do you think you will end up spending?

kerrypod

893bet wrote: »

How much do you think you will end up spending?

My budget is 150k for finished habitable house, however did another check on the costs today and it will probably take another 50k to finish it!

893bet

kerrypod wrote: »

My budget is 150k for finished habitable house, however did another check on the costs today and it will probably take another 50k to finish it!

I was asking the other fella as he is building a similar size house to you.

200k is still tight enough! I would urge you to educate yourself on Airtightness, ventilation, insulation and cold bridging, before you go any further.

murphy31ie

Sorry I forgot to say it will probably cost 250k. Have you considered things like electricity connection 2-3k etc,

To be honest I think I did well to keep it to 250 but I have geothermal with ufh which is a good bit dearer than the traditional heating methods.