SAP fail mainly due to walls

[WWilts]

What would you do? (Jargon used here, but pls don't assume I understand it or know all about these matters)

SAP fail mainly due to walls being 0.27

Architect design for cavity walls:

Block inner 100mm Celcon Jumbo blok hi strength with thin joint mortar
Dritherm 37 insulation 100mm
Brick outer 100mm (reconst stone on front elevation)

Windows & door double glazed. 2 rooflights, one west facing in entrance porch. Other north facing in attic, mainly to allow light to storage space & allow ventilation/air changes on hot days.

SAP consultant suggested increase loft insulation from 300 to 400mm, and use Megaflo cylinder OR combi for hot water. Then if air test set to 4.0, can pass without changing walls

What would you do?
Context: We are likely to have to move in a few yrs, so cost-effectiveness over a 5 yr horizon is important to us. Both installation and running costs over 5 years. Expense welcome only if it will boost the eventual selling price.

Idea so far:

Better walls (if planner will permit render, then cavity wall outer leaf Celcon Jumbo blok Solar grade outer leaf with thin joint mortar + monocouche render)
Might ease the pressure on air test / boiler spec / thickness of attic insulation (insulation welcome, but freedom to stay with 300mm insulation in parts of attic also desired)

You might well spot options to which we are blind



 

[the_r_sole]

what window and door spec have you got? If they're are big areas of glass bringing the uvalue down on those would give you a good boost on sap

heating system is somewhere else to look, walls give you an incremental increase but how far is it failing? 

[PeterW]

Make the cavity 150mm and use blown beads. 
 

100mm can no longer pass unless you use insulated plasterboard - your architect should know that. 
 

Ditch the jumbos with thin joint - they are expensive crap with expensive wall ties and brickies hate them. Go for a standard block and mortar.  
 

 

[ProDave]

And aim for an air test of much better than 4.0.  Detail it properly and get a much lower actual air test value.

 

Are you fitting mvhr?

 

What do you want from the house?  A really comfortable house that needs very little heating, or as cheap as possible build to just scrape through building regs and have higher heating costs?

[A_L]

1 hour ago, WWilts said:

Dritherm 37 insulation 100mm

 

Changing to Dritherm 32 could make more carbon savings than adding 100mm to loft insulation if walls have greater m² than roof and improve wall U-value to about 0.24

Edited January 29, 2021 by A_L
remove typo

[Conor]

Your architect needs a slap for coming up with such a poorly performing design that isn't even meeting minimum standards.

 

Even though you'll be moving on in a few years, please bear in mind your house will be around for another 100 years or more. You should be aiming to blow through the SAP requirements, not scrape though.

 

As above, make cavities 150mm wide, put in 150mm insulation in the floors, 400mm in the loft and consider higher performing windows and doors. And airtightness, makes a huge difference. It will of course add some cost to your build, but you'll have a much more comfortable house and a better legacy for the future.

Edited January 29, 2021 by Conor

[Temp]

+1 

 

You can aim for better air tightness but I wouldn't rely on achieving it.

[MikeGrahamT21]

Calculations incorrect??

 

ubakus.com tells me 0.26U with 40 grade wool insulation

with 32 grade wool insulation this goes to 0.22U

[WWilts]

2 hours ago, the_r_sole said:

what window and door spec have you got? If they're are big areas of glass bringing the uvalue down on those would give you a good boost on sap

heating system is somewhere else to look, walls give you an incremental increase but how far is it failing? 

Double glazed
Underfloor heating downstairs & in bathrooms upstairs. Radiators upstairs

[WWilts]

2 hours ago, PeterW said:

Ditch the jumbos with thin joint - they are expensive crap with expensive wall ties and brickies hate them. Go for a standard block and mortar. 

That's an angle not considered before. Quickly reaching weathertight stage was incentive for thin joint blockwork. Perhaps it's a bad idea?

 

[WWilts]

1 hour ago, ProDave said:

What do you want from the house?  A really comfortable house that needs very little heating, or as cheap as possible build to just scrape through building regs and have higher heating costs?

Somewhere between, because of 5 yr horizon.
Minimise costs of build + 5yr running, while still making it attractive to the next occupants.

[WWilts]

1 hour ago, Conor said:

make cavities 150mm wide, put in 150mm insulation in the floors, 400mm in the loft and consider higher performing windows and doors.

Thanks

[Iceverge]

5 years is a long time and a lot could change by then. 

 

In terms of energy saving the lowest hanging fruits to improve on building regs are. 

 

1.Triple Glazing

2. MVHR

3. Airtightness

 

Added insulation is only an incremental gain in comparison. 

 

You could probably ditch the rads upstairs too in all but the bathrooms. 

 

 

 

 

 

 

Edited January 29, 2021 by Iceverge

[WWilts]

39 minutes ago, MikeGrahamT21 said:

ubakus.com tells me 0.26U with 40 grade wool insulation

with 32 grade wool insulation this goes to 0.22U

We're out of our depth on this.
But we're in favour of boosting SAP scores. Just don't want to go silly with the spend.

[WWilts]

2 minutes ago, Iceverge said:

You could probably ditch the rads upstairs too in all but the bathrooms. 

Underfloor heating upstairs? 

[Iceverge]

Just now, WWilts said:

Underfloor heating upstairs? 

No heating at all upstairs. In a new house you won't need it. 

[ProDave]

No mention of renewables like solar PV?

[ProDave]

Just now, Iceverge said:

No heating at all upstairs. In a new house you won't need it. 

Only if insulated properly and nicely air tight.  I suspect this house might want some.

[Jason L]

22 minutes ago, ProDave said:

Only if insulated properly and nicely air tight.  I suspect this house might want some.

sorry, I'm just high jacking the tread for my house, i have a design SAP rating of A 93, with MVHR and i will try and make it super air tight,

do you think I'm not going to need any heating on the first floor and in the attic bedroom,  just towel rails in the shower rooms ?

[Iceverge]

25 minutes ago, ProDave said:

Only if insulated properly and nicely air tight.  I suspect this house might want some.

Yeah, maybe you're right. Scraping through the SAP by hook or by crook isn't a great start. 

[WWilts]

32 minutes ago, ProDave said:

No mention of renewables like solar PV?

True. Looking into it. 

[Iceverge]

3 hours ago, Jason L said:

sorry, I'm just high jacking the tread for my house, i have a design SAP rating of A 93, with MVHR and i will try and make it super air tight,

do you think I'm not going to need any heating on the first floor and in the attic bedroom,  just towel rails in the shower rooms ?

I think you'll be fine. 

[Gus Potter]

7 hours ago, WWilts said:

What would you do? (Jargon used here, but pls don't assume I understand it or know all about these matters)

SAP fail mainly due to walls being 0.27

Architect design for cavity walls:

Block inner 100mm Celcon Jumbo blok hi strength with thin joint mortar
Dritherm 37 insulation 100mm
Brick outer 100mm (reconst stone on front elevation)

Windows & door double glazed. 2 rooflights, one west facing in entrance porch. Other north facing in attic, mainly to allow light to storage space & allow ventilation/air changes on hot days.

SAP consultant suggested increase loft insulation from 300 to 400mm, and use Megaflo cylinder OR combi for hot water. Then if air test set to 4.0, can pass without changing walls

What would you do?
Context: We are likely to have to move in a few yrs, so cost-effectiveness over a 5 yr horizon is important to us. Both installation and running costs over 5 years. Expense welcome only if it will boost the eventual selling price.

Idea so far:

Better walls (if planner will permit render, then cavity wall outer leaf Celcon Jumbo blok Solar grade outer leaf with thin joint mortar + monocouche render)
Might ease the pressure on air test / boiler spec / thickness of attic insulation (insulation welcome, but freedom to stay with 300mm insulation in parts of attic also desired)

You might well spot options to which we are blind

@Jason f
 

Consider the simple stupid.

 

Roughly, as a ball park the labour cost on a new build is about a third for standard stuff, on a small extension this can easily touch 50%. (see R_Sole etc for good info) Some BH members are "in the trade" and can get a good discount and avoid the uplift due to complexity.  But if you are starting out then maybe you want to make it easy to build. More local builders will be interested in pricing if it looks simple and they feel they can make a profit with less risk. The less risk they perceive the lower your price will often be.  See what prices you get back with simple construction (avoid thin joints) then compare this with making it more complex.. remember that often you are working on a small scale unless you are a very wealthy Client.

 

It's hard to do but you need to look at this in the round.. all the folk on your team should be pulling together. One big problem is that you often can't get a builder to price realistically without a descent spec.. it's catch 22. But starting with a simple spec can be attractive for a builder.. and once they are interested you can explore the cost of upping the spec. Good experienced designers will cost more but you get what you pay for and the really good ones will invest in you and give more than they take.. provided you pay their bill on time.

 

To get the higher strength in a block you need more conductive material (density), less air.. air can't transmit load in this context. The thin joints offset this but you reduce your options regarding the builders who want to take the job on as they have to be much more accurate and this take time = extra cost.

 

For me I would start with basic construction.. see how much that costs. Then you can start adding on the extra bells and whistles that appeal to you, energy saving etc, fire risk and so on.

 

@Jason L"sorry, I'm just high jacking the tread for my house, i have a design SAP rating of A 93, with MVHR and i will try and make it super air tight,

do you think I'm not going to need any heating on the first floor and in the attic bedroom,  just towel rails in the shower rooms"

 

Jason , it may be worthwhile having a chat with your designer about how the building is prevented from moving from left to right say (on the drawings) when the wind blows. You don't have too much on the ground floor to achieve structural stability by the looks of things. It may be a good idea to make sure you have a good handle on how the structure will work, then you can plan the services. If you don't do it this way then the saving on energy performance you think you make make may not be realised as you could end up with beams etc in the way of your ducts... sounds painful

[WWilts]

11 minutes ago, Gus Potter said:

For me I would start with basic construction.. see how much that costs. Then you can start adding on the extra bells and whistles that appeal to you, energy saving etc,

Yes, basic cavity wall was the original design. Failed SAP. Interested in improving energy efficiency in reasonably cost-effective ways, anyhow. For SAP and otherwise too.

[Jason L]

39 minutes ago, Gus Potter said:

Consider the simple stupid.

 

Roughly, as a ball park the labour cost on a new build is about a third for standard stuff, on a small extension this can easily touch 50%. (see R_Sole etc for good info) Some BH members are "in the trade" and can get a good discount and avoid the uplift due to complexity.  But if you are starting out then maybe you want to make it easy to build. More local builders will be interested in pricing if it looks simple and they feel they can make a profit with less risk. The less risk they perceive the lower your price will often be.  See what prices you get back with simple construction (avoid thin joints) then compare this with making it more complex.. remember that often you are working on a small scale unless you are a very wealthy Client.

 

It's hard to do but you need to look at this in the round.. all the folk on your team should be pulling together. One big problem is that you often can't get a builder to price realistically without a descent spec.. it's catch 22. But starting with a simple spec can be attractive for a builder.. and once they are interested you can explore the cost of upping the spec. Good experienced designers will cost more but you get what you pay for and the really good ones will invest in you and give more than they take.. provided you pay their bill on time.

 

To get the higher strength in a block you need more conductive material (density), less air.. air can't transmit load in this context. The thin joints offset this but you reduce your options regarding the builders who want to take the job on as they have to be much more accurate and this take time = extra cost.

 

For me I would start with basic construction.. see how much that costs. Then you can start adding on the extra bells and whistles that appeal to you, energy saving etc, fire risk and so on.

 

@Jason L"sorry, I'm just high jacking the tread for my house, i have a design SAP rating of A 93, with MVHR and i will try and make it super air tight,

do you think I'm not going to need any heating on the first floor and in the attic bedroom,  just towel rails in the shower rooms"

 

Jason , it may be worthwhile having a chat with your designer about how the building is prevented from moving from left to right say (on the drawings) when the wind blows. You don't have too much on the ground floor to achieve structural stability by the looks of things. It may be a good idea to make sure you have a good handle on how the structure will work, then you can plan the services. If you don't do it this way then the saving on energy performance you think you make make may not be realised as you could end up with beams etc in the way of your ducts... sounds painful

Thanks for your comments it’s a timber a frame and I’ll talk to them about it, I do keep wondering what stops a timber frame from blowing away !   Ref beams  there will be one over the middle of the kitchen, and the other side of that it’s a vaulted ceiling,  that’s the only place I can see being an issue getting the duct to the dining room.  Cheers.