Need help with building calculations

mrsWhippy

Hi there,

I want to have the following information before I commit to a particular build fabric & insulation level.

I'd like to be able to calculate the impact and cost of increasing the u-values of the walls and roof, the resulting reduction in energy requirements, and the knock on effect on the cost required to heat that space using one of two schemes. Basically I want to determine the 'sweet spot' between insulation and cost.

I have the DEAP software and 2 of the BER XML files - would this be a good starting point? If not, who should be able to give me these figures? Architect? BER Assessor?

Help! My head is melted. And I don't feel it'd be wise to commit to any insulation or heating scheme until I can see these figures in B&W.

Thanks

BryanF

Passive house software package is the only user friendly methodolgy I know of acturately predicting heat loss/gain

Do you have tender/construction drawings prepared?

mrsWhippy

BryanF wrote: »

Passive house software package is the only user friendly methodolgy I know of acturately predicting heat loss/gain

Do you have tender/construction drawings prepared?

No, not yet Bryan. That's our next step. We haven't decided final build fabric yet which is why I wanted to explore our options before the decision has to be made.

There are so many knock on effects to the build costs when increasing cavity size or improving insulation values etc, I'm finding it so difficult to get informed enough to make an educated decision!!! :(

We have a QS estimate at the moment for 200mm cavity with eco-bead.

BryanF

IMO this is not only a cost issue but a quality issue

Quality in terms of:

Builder: lack of education , lack of care & attention , lack of clarity on pricing documents, 'this is what I always do'
Architect: lack of understanding of construction sequencing, and practicalities of achieving quality on certain cheaper construction methods, lack of clarity/ quality of detailed drawings
Client: lack of foresite to accept that there are other factors apart from cost to be considered - ie quality, comfort, health, longevity, environmental etc

mrsWhippy

I get your point Bryan, but I also don't get the point of the point

I can't educate the builder. I can only try hire someone reputable who has a track record of building to decent specs.
We don't have construction drawings yet so can't comment on the architect's knowledge here either.

I do understand the other factors of course which is why i'm trying to tease these out now, but on the other hand I can't magic money out of thin air either so cost is a huge part of the decision making process (unfortunately!)

Criddy

Have you considered a timber frame company at all? Some of them are genuinely nice people.

mrsWhippy

Criddy wrote: »

Have you considered a timber frame company at all? Some of them are genuinely nice people.

We actually haven't, apart from SIP.

We want a concrete slab on the first floor so apart from SIP, that wouldn't be an option with TF I guess?

Criddy

Very true. I am obviously unaware of finer details, why a concrete slab? Are posi joists (the open metal web joist things) not a viable option?

mrsWhippy

Criddy wrote: »

Very true. I am obviously unaware of finer details, why a concrete slab? Are posi joists (the open metal web joist things) not a viable option?

I am also unaware of the finer details which is why this process has been so bloody stressful!

Sound insulation, fire proofing, UFH and block walls on first floor - what are those posi joists? (googling now...)

DeeJunFan

The only thing you can do really is to educate yourself.

If you are totally set on Block build then your at least only tweaking the options.

Your starting point will need to be the building regs. I'm in NI so i'm not as restricted.

To be honest i found that increasing wall insulation past about 0.17 wasn't really going to give a lifetime payback. I know you don't have that option but i wouldn't go past what you have to on wall insulation.

I decided to put the extra money into windows, going for the best performance i could afford (PH cert, 3G)

For example paying say 2-3K extra to get walls from 0.17 to say 0.12 (that was my rough estimate based on ties, insulation, builder hassle) i would have probably only saved around 100 (stg) per year on heating costs. but spending 3k extra on windows to bring them from 1.3 to around 0.8 was going to save around 5-6 hundred per year.

It makes sense you spend 2k on walls to reduce uvalue by 0.05 but you reduce windows by 0.5 so the performace improvement for the same investment is a factor of 10.

I spent more on floor and roof insulation as they are more important especially with UFH so they are both 0.10

Air-tightness is the one thing you can really "model" its going to be down to who does it and how well they do it.

Thermal bridging is something you are going to be relying on your architect for. Making sure all the details are thermal bridge free. (I had to go back to mine on a few) This means you will need to be able to see the thermal bridges. Or ask.

BryanF

mrsWhippy wrote: »

I get your point Bryan, but I also don't get the point of the point

I can't educate the builder. I can only try hire someone reputable who has a track record of building to decent specs.
We don't have construction drawings yet so can't comment on the architect's knowledge here either.

I do understand the other factors of course which is why i'm trying to tease these out now, but on the other hand I can't magic money out of thin air either so cost is a huge part of the decision making process (unfortunately!)

i appreciate your predicament
My only point was a focus solely on costs impacts quality.
You should be relying on your architect with support from the Qs to make this decision, but I stand by my post above - the phpp software is the best way to answer your question (in conjunction with arch & Qs)

mrsWhippy

Thank you DeeJunFan! That is exactly the info I'm after.

For example paying say 2-3K extra to get walls from 0.17 to say 0.12 (that was my rough estimate based on ties, insulation, builder hassle) i would have probably only saved around 100 (stg) per year on heating costs.

How did you calculate this?

With regard to the thermal bridges, I've already confirmed that the detailing in the construction drawings will all specify the junctions as per the DoE 'Acceptable Construction Details' - should this be enough (in theory)?

DeeJunFan

mrsWhippy wrote: »

Thank you DeeJunFan! That is exactly the info I'm after.

For example paying say 2-3K extra to get walls from 0.17 to say 0.12 (that was my rough estimate based on ties, insulation, builder hassle) i would have probably only saved around 100 (stg) per year on heating costs.

How did you calculate this?

I got a quote for different sized wall ties, If you are going for a 200mm cavity you will need at leave 350mm possibly 375mm ties if you go up to 250m cavity then you need 450/475mm ties.

From memory (i cant check the exact figures) i had worked out each additional 25mm of beads would be around 500 (stg). Then once you go over a certain size cavity the brick layers wont work Over hand (building both walls from one side) so need to do each leaf from the wall side, so that takes them extra time.

I think for you the wall uvalue that you must go for is over and above the sweetspot so i would just go with reg value for walls and put money into other fabric.

mrsWhippy

DeeJunFan wrote: »

I got a quote for different sized wall ties, If you are going for a 200mm cavity you will need at leave 350mm possibly 375mm ties if you go up to 250m cavity then you need 450/475mm ties.

From memory (i cant check the exact figures) i had worked out each additional 25mm of beads would be around 500 (stg). Then once you go over a certain size cavity the brick layers wont work Over hand (building both walls from one side) so need to do each leaf from the wall side, so that takes them extra time.

I think for you the wall uvalue that you must go for is over and above the sweetspot so i would just go with reg value for walls and put money into other fabric.

Interesting, thanks.

Our BER specified 0.2 for the walls. I had suggested increasing the cavity to 200mm full-fill eco-bead in order to reduce this to 0.15. I doubt we'll be aiming for any better than this.

DeeJunFan

mrsWhippy wrote: »

DeeJunFan wrote: »

I got a quote for different sized wall ties, If you are going for a 200mm cavity you will need at leave 350mm possibly 375mm ties if you go up to 250m cavity then you need 450/475mm ties.

From memory (i cant check the exact figures) i had worked out each additional 25mm of beads would be around 500 (stg). Then once you go over a certain size cavity the brick layers wont work Over hand (building both walls from one side) so need to do each leaf from the wall side, so that takes them extra time.

I think for you the wall uvalue that you must go for is over and above the sweetspot so i would just go with reg value for walls and put money into other fabric.

Interesting, thanks.

Our BER specified 0.2 for the walls. I had suggested increasing the cavity to 200mm full-fill eco-bead in order to reduce this to 0.15. I doubt we'll be aiming for any better than this.

ok so you BER was for 150mm cavity full fill with beads.

Then you are pretty much in the same situation as i was. If you wanted you could just split the difference and go 175mm cavity. More money and get you to 0.17 ish.

If you are looking at timber frame they will all be quoting better wall figures but i personally didn't see the benefit of beefing up the walls anymore. given the heat loss will be much higher from the windows

mrsWhippy

Good tip, thanks.

Also like the block thermal mass properties, and of course the option to have concrete slab on first floor, so we've sort of eliminated traditional TF construction at this stage.

Will look at floor and roof insulation in more detail, cheers.

DeeJunFan

mrsWhippy wrote: »

Good tip, thanks.

Also like the block thermal mass properties, and of course the option to have concrete slab on first floor, so we've sort of eliminated traditional TF construction at this stage.

Will look at floor and roof insulation in more detail, cheers.

Are you planning for UFH? If so then i would suggest as good as you can on the floor. I'm doing 200m PIR if your architect or anyone specs PUR, then i would push back as its double the price for a very slight improvement in performance.

for the roof just stick as much of the cheapest stuff you can get up there say 500mm of rock wool. Unless you are going warm roof. Then thats a bit more complicated.