new build insulation, airtightness question

gooner99

Hi.

I've put our plans for our 140sqm story and a half out for tender to a couple of timber frame companies. My brother in law (QS) has done up a price based on the quotes I received back and also for a basic traditional cavity build. The cavity build was coming in cheapest, but bear in mind that the insulation levels in his calcs were not a good as the timber frame. I am still open to the timber frame, but feel I should at least properly explore block built.

I want to take it a little further on the block built side and get some quotes from a few good builders that I have shortlisted. I have tender docs from my brother in law to give to them, but what I am lacking is a clear insulation and air-tightness spec to accompany it with. I fear that if I simply advise that it must be insulated and airtight to the current reg they will simply quote for standard cavity with board or beads and internal insulated boards. I want to steer clear of this and have all the insulation in the cavity by way of wide cavity with full fill board or blown beads.

Could any of you guys give me a spec for floor, wall and roof insulation that will at least meet the current regs. At least then they will all be singing of the same hymn sheet and I can compare like for like.

I am leaning towards the idea of 150mm cavity with full fill boards or a wide cavity with blown beads that will give good results without being too difficult to build. But I have no idea what the floor and roof insulation should be.

Please let me know if you would like any further info and thanks for your help.

Gumbo

gooner99 wrote: »

Could any of you guys give me a spec for floor, wall and roof insulation that will at least meet the current regs. At least then they will all be singing of the same hymn sheet and I can compare like for like.

I am leaning towards the idea of 150mm cavity with full fill boards or a wide cavity with blown beads that will give good results without being too difficult to build. But I have no idea what the floor and roof insulation should be.

Please let me know if you would like any further info and thanks for your help.

This is what your BER Assessor will calculate. All the elements need to be taken together. Your wall insulation values need to be inputted into the DEAP software along with your floor details to ensure all round compliance. The BER needs your floor plans to work our areas, volumes and perimeters.

I think it might be wise to engage one at this stage.

delfagio

your best bet would be to get a BER Assessor along with the Architect/Designer to sit down with you, work out what U-Values you want to achieve and they will work out what amounts of insulation you will need, type of insulation required, and methods on how to achieve the airtightness you require. really that's the best bet, then include for this in your tender docs for contractors to price for,

bit of a vague answer I know but it's the best way that you can get the answers you need,

hope it helps

gooner99

Thanks Guys. Will of course get a BER done when we decide between block and timber frame.

Was just going to do a basic spec in order to tender for block build to see how it stacks up against timber frame. I know it can be comparing apples with oranges and I understand there are quite a lot of elements to look at, insulation airtightness, ventilation, windows.

Would anyone have a sample of what they did recently in terms of floor, wall and roof insulation in a block built house. You can PM me if you prefer.

Thanks again all.

BryanF

This is Typcially something an architect/ arch tech gets paid to work out.

gooner99

No problem. I understand.

JimmyMW

gooner99 wrote: »

Hi.

I've put our plans for our 140sqm story and a half out for tender to a couple of timber frame companies. My brother in law (QS) has done up a price based on the quotes I received back and also for a basic traditional cavity build. The cavity build was coming in cheapest, but bear in mind that the insulation levels in his calcs were not a good as the timber frame. I am still open to the timber frame, but feel I should at least properly explore block built.

I want to take it a little further on the block built side and get some quotes from a few good builders that I have shortlisted. I have tender docs from my brother in law to give to them, but what I am lacking is a clear insulation and air-tightness spec to accompany it with. I fear that if I simply advise that it must be insulated and airtight to the current reg they will simply quote for standard cavity with board or beads and internal insulated boards. I want to steer clear of this and have all the insulation in the cavity by way of wide cavity with full fill board or blown beads.

Could any of you guys give me a spec for floor, wall and roof insulation that will at least meet the current regs. At least then they will all be singing of the same hymn sheet and I can compare like for like.

I am leaning towards the idea of 150mm cavity with full fill boards or a wide cavity with blown beads that will give good results without being too difficult to build. But I have no idea what the floor and roof insulation should be.

Please let me know if you would like any further info and thanks for your help.

Hi gooner99,

I have done this type of comparison recently myself and the block option worked out significantly cheaper comparing like for like in terms of U-Value, from my investigation of timber frame the only advantage is the speed of construction imo. Hope this helps. PM me if you want more specifics.

Regards
J

galwaytt

JimmyMW wrote: »

Hi gooner99,

I have done this type of comparison recently myself and the block option worked out significantly cheaper comparing like for like in terms of U-Value, from my investigation of timber frame the only advantage is the speed of construction imo. Hope this helps. PM me if you want more specifics.

Regards
J

Straight up: I'm in the 'TF' business, and your comment is the one I see most often quoted, but in practice it does not always follow suit. This is one reason why I try and get clients' finished costs for builds, when they're finished - it helps me see where 'we' are in the scheme of things.

Your comment about speed does have a measurable cost saving to the client, so should not be discounted. Imagine if you're renting whilst your new house is built - to be in your house in 5 or 6 months, instead of 12 months +, at the current prevailing rental rates is not to be sneezed at..........

I have only 2 prices back from clients for finished builds, for 2015 so far: 237m2 in the N.E. for €1075/m2 (finishing March) and 299m2 in the N.W. came at 1000/m2 (completed late 2014, and in for Christmas). I'm open to correction here, but I think that's competitive. Remember that even of those costs, only approx 25% are attributable to the TF company........

I note OP only mentions u-value, and this is (half) the problem. Airtightness is so important it's not funny, really, and in this day & age is at least as important as u-value - and arguably more. Here (all) TF has an advantage imho.

Then there's the new BCMS costs that you save in TF.

When you factor that in, then TF in general (and I include all other TF companies here), should be price competitive with anything.

JimmyMW

galwaytt wrote: »

Straight up: I'm in the 'TF' business, and your comment is the one I see most often quoted, but in practice it does not always follow suit. This is one reason why I try and get clients' finished costs for builds, when they're finished - it helps me see where 'we' are in the scheme of things.

Your comment about speed does have a measurable cost saving to the client, so should not be discounted. Imagine if you're renting whilst your new house is built - to be in your house in 5 or 6 months, instead of 12 months +, at the current prevailing rental rates is not to be sneezed at..........

I have only 2 prices back from clients for finished builds, for 2015 so far: 237m2 in the N.E. for €1075/m2 (finishing March) and 299m2 in the N.W. came at 1000/m2 (completed late 2014, and in for Christmas). I'm open to correction here, but I think that's competitive. Remember that even of those costs, only approx 25% are attributable to the TF company........

I note OP only mentions u-value, and this is (half) the problem. Airtightness is so important it's not funny, really, and in this day & age is at least as important as u-value - and arguably more. Here (all) TF has an advantage imho.

Then there's the new BCMS costs that you save in TF.

When you factor that in, then TF in general (and I include all other TF companies here), should be price competitive with anything.

Hi Galwaytt,

I agree that time on site can be a cost saving, however this is specific to the clients situation, for me this was not a consideration. Additionally there is no way that TF is 6 to 7 months quicker on site compared to block work, as your figures suggest.

For me I am happy I have considered all the cost differences between the two methods of construction, U-Values, thermal mass, heating systems, airtightness etc. My investigation into this for "my project" showed that the concrete block option is between €4-6k cheaper than timber frame and to be honest I have a preference for concrete block anyway due to things like shrinkage and sound transmittance etc relating to TF, therefore if block work came anyway close, even if it was slightly more expensive I was going for block work. Please note I had a chartered QS complete this comparison for me, this is not me looking at a few quotes and making a rash decision.

Those prices seam quite competitive, however it has been discussed on numerous threads here before, final prices per m2 are highly dependent on finish therefore IMO that is not an accurate depiction of the cost difference between TF and equivalent block work.

I completely agree regarding the importance of Air Tightness, and I do accept that achieving an equivalent airtightness with block work is more difficult, however with good on site supervision it should be achievable. The TF advantage regarding airtightness was definitely not enough of an advantage to sway my choice.

Can you expand on your statement regarding BCMS costs?

galwaytt

JimmyMW wrote: »

Hi Galwaytt,

I agree that time on site can be a cost saving, however this is specific to the clients situation, for me this was not a consideration. Additionally there is no way that TF is 6 to 7 months quicker on site compared to block work, as your figures suggest.

For me I am happy I have considered all the cost differences between the two methods of construction, U-Values, thermal mass, heating systems, airtightness etc. My investigation into this for "my project" showed that the concrete block option is between €4-6k cheaper than timber frame and to be honest I have a preference for concrete block anyway due to things like shrinkage and sound transmittance etc relating to TF, therefore if block work came anyway close, even if it was slightly more expensive I was going for block work. Please note I had a chartered QS complete this comparison for me, this is not me looking at a few quotes and making a rash decision.

Those prices seam quite competitive, however it has been discussed on numerous threads here before, final prices per m2 are highly dependent on finish therefore IMO that is not an accurate depiction of the cost difference between TF and equivalent block work.

I completely agree regarding the importance of Air Tightness, and I do accept that achieving an equivalent airtightness with block work is more difficult, however with good on site supervision it should be achievable. The TF advantage regarding airtightness was definitely not enough of an advantage to sway my choice.

Can you expand on your statement regarding BCMS costs?

I'm afraid that TF is quicker - there's no other way to put it. I can cite various examples, from simple bungalow to complex (other), and they have all been delivered to completion months ahead of what can be done site-built.

E.g. 350m2, large single storey, delivered in the last week July, moved into, complete, 3rd week of December.
110m2 semi-d: 12 weeks intoto (for a builder).

This week we started a 192m2 2-storey in Galway, last Monday. Roof going on next Monday - snow yesterday didn't help. If it slows down now, it will be because of follow-on trades (or the organising of them). If organised well, there's no reason he can't be living in it very quickly. My experience would not be uncommon in the wider TF business, all other companies included.

Pricing for any house, in any method, is hugely contingent on specification, you're right, and also whether self-build, project-managed, or contractor built. For a QS set of figures to be accurate, you have to give him all that relevant info too.

BCMS costs are the preserve of those doing it, but suffice to say that by using any off-site method, which have always had independent structural, warranted and 3rd party certification, there are costs you won't be incurring that you will incur in a site-build. Hence the DC/AC exposure to risk is lower, and that should be reflected in fees.

JimmyMW

galwaytt wrote: »

I'm afraid that TF is quicker - there's no other way to put it. I can cite various examples, from simple bungalow to complex (other), and they have all been delivered to completion months ahead of what can be done site-built.

E.g. 350m2, large single storey, delivered in the last week July, moved into, complete, 3rd week of December.
110m2 semi-d: 12 weeks intoto (for a builder).

This week we started a 192m2 2-storey in Galway, last Monday. Roof going on next Monday - snow yesterday didn't help. If it slows down now, it will be because of follow-on trades (or the organising of them). If organised well, there's no reason he can't be living in it very quickly. My experience would not be uncommon in the wider TF business, all other companies included.

Pricing for any house, in any method, is hugely contingent on specification, you're right, and also whether self-build, project-managed, or contractor built. For a QS set of figures to be accurate, you have to give him all that relevant info too.

BCMS costs are the preserve of those doing it, but suffice to say that by using any off-site method, which have always had independent structural, warranted and 3rd party certification, there are costs you won't be incurring that you will incur in a site-build. Hence the DC/AC exposure to risk is lower, and that should be reflected in fees.

I have already accepted that TF is quicker, but your quoting figures relating to time that cannot be attributed to the fact that the construction is TF alone.

Simply look at it this way if you take a house of 2500sqf story and a half. That will contain between 12000 and 15000 blocks depending on layout, assuming a 5 man block laying crew with one of them being a laborer, 1 man will lay 200 blocks in a day if tended at his ease, that’s between 15-19 days for that crew 3-4 weeks! Give another week to stand a roof and get felted and lattes as you would have done, allow another 3 week for instillation of first floor and plaster boarding the ceilings the give an electrician another week for chasing walls that he would not have to do in TF and give a week to pump the cavity.

The work for rising walls and floors will take relatively the same time regardless of construction above therefore I have not considered these items. As outlined above the block work in the example will take 10 weeks assuming the larger amount for blocks, but just for the sake of it give it 11 weeks allowing a 10% overrun VS say your TF would I be ok to give it a week with a big crew to stand it and roof it including felt and battens? And say another week for the block work skin? That’s a difference of 9 weeks and to be fair I have overestimated the time required here for the block work.

I know I have not taken into account weather conditions above and that can definitely delay the block work option, however I just can’t see where you could get nearly another 5 months on top of what I have said above?

That’s what I taught you meant by your comment regarding BCMS however I said I would seek clarification from you prior to commenting. I have spoken with many people who are currently in the role of DC/AC and not one required to know the construction type prior to quoting for a job, therefore IMO the cost saving relating to the reduced exposure of the timber frame company will be seen in someone else’s pocket other than the client.

All in all anyway its entirely up to the individual themselves as there are 1000’s of ways to construct any building but, IMO, regarding domestic construction, I believe that block work is the more preferable option, and is cheaper than TF from my investigation. And yes just in case you think I am forgetting, TF is quicker and easier to achieve a good air tightness result.

gruby

gooner99 wrote: »

Hi.

I've put our plans for our 140sqm story and a half out for tender to a couple of timber frame companies. My brother in law (QS) has done up a price based on the quotes I received back and also for a basic traditional cavity build. The cavity build was coming in cheapest, but bear in mind that the insulation levels in his calcs were not a good as the timber frame. I am still open to the timber frame, but feel I should at least properly explore block built.

I want to take it a little further on the block built side and get some quotes from a few good builders that I have shortlisted. I have tender docs from my brother in law to give to them, but what I am lacking is a clear insulation and air-tightness spec to accompany it with. I fear that if I simply advise that it must be insulated and airtight to the current reg they will simply quote for standard cavity with board or beads and internal insulated boards. I want to steer clear of this and have all the insulation in the cavity by way of wide cavity with full fill board or blown beads.

Could any of you guys give me a spec for floor, wall and roof insulation that will at least meet the current regs. At least then they will all be singing of the same hymn sheet and I can compare like for like.

I am leaning towards the idea of 150mm cavity with full fill boards or a wide cavity with blown beads that will give good results without being too difficult to build. But I have no idea what the floor and roof insulation should be.

Please let me know if you would like any further info and thanks for your help.

for the sake of getting quotes I think enough would be to :
1. go to environ.ie > building standards> part L to get required U values ( 0.16 for roof, 0.15 for floor with UFH, etc...)
2. google "how to calculate U value", there are many online formulas/ guides for everything and as result you will have the rough required thickness of insulation needed
those figures will be a minimum, go for 30-50% increase as this going to be your house, and you want the average and not the worst case spec

galwaytt

JimmyMW wrote: »

I have already accepted that TF is quicker, but your quoting figures relating to time that cannot be attributed to the fact that the construction is TF alone.

Simply look at it this way if you take a house of 2500sqf story and a half. That will contain between 12000 and 15000 blocks depending on layout, assuming a 5 man block laying crew with one of them being a laborer, 1 man will lay 200 blocks in a day if tended at his ease, that’s between 15-19 days for that crew 3-4 weeks! Give another week to stand a roof and get felted and lattes as you would have done, allow another 3 week for instillation of first floor and plaster boarding the ceilings the give an electrician another week for chasing walls that he would not have to do in TF and give a week to pump the cavity.

The work for rising walls and floors will take relatively the same time regardless of construction above therefore I have not considered these items. As outlined above the block work in the example will take 10 weeks assuming the larger amount for blocks, but just for the sake of it give it 11 weeks allowing a 10% overrun VS say your TF would I be ok to give it a week with a big crew to stand it and roof it including felt and battens? And say another week for the block work skin? That’s a difference of 9 weeks and to be fair I have overestimated the time required here for the block work.

I know I have not taken into account weather conditions above and that can definitely delay the block work option, however I just can’t see where you could get nearly another 5 months on top of what I have said above?

That’s what I taught you meant by your comment regarding BCMS however I said I would seek clarification from you prior to commenting. I have spoken with many people who are currently in the role of DC/AC and not one required to know the construction type prior to quoting for a job, therefore IMO the cost saving relating to the reduced exposure of the timber frame company will be seen in someone else’s pocket other than the client.

All in all anyway its entirely up to the individual themselves as there are 1000’s of ways to construct any building but, IMO, regarding domestic construction, I believe that block work is the more preferable option, and is cheaper than TF from my investigation. And yes just in case you think I am forgetting, TF is quicker and easier to achieve a good air tightness result.

Nothing wrong with your timetable - on paper. All i can quote is my own direct experience.

And that's the advantage of all off site building - not just TF btw - time. Factory time is measured, accurate, consistent. Site time is elastic. It's the nature of building, of people, of weather. And all of it is measured in €€€€.

And if your DC/AC does not allow for the costs he does NOT incur by using (any) offsite system, then you're paying for some of that work twice over. In other words your DC/AC is charging for stuff he doesn't have to do. In which case I'd ask does he understand the project ?? And if he's not giving you the benefit of his saving, it's his pocket the saving is being put in. What would you accept that ?

Calahonda52

gooner99 wrote: »

Hi.

....
I am leaning towards the idea of 150mm cavity with full fill boards or a wide cavity with blown beads that will give good results without being too difficult to build. But I have no idea what the floor and roof insulation should be....

Re this
without being too difficult to build.
The key word that is missing here is right.

I am not knocking block build (BB) but you just cannot get the same level of comfort with a cavity block build as with a TF build for the simple reason that you can't see what exactly has been done during the build.
Its just too hard to get right.
With TF you are relying on QC in the factory to get the panels made right and the insulation fitted properly if thats what you go for or go for insulation added on site.
At least you can see whats happening.

Even from the aspect of the worker: do u think a guy working in a factory, in out of therein and wind, will on balance be more inclined to do the job properly that on some windily wet site with the sheets of insulation blowing around in the wind and getting corners broken off or distorted by the cavity ties


Then as galway tt has stated Air Tightness (A/T) is critical and can be easier to address in TF than BB

It can be done in either but in BB it needs to be sequenced more carefully than with TF.

Forget about Part L, look at the insulation levels and construction details for Passiv House.
Consider MHVR and plan it from day one rather than as an afterthought.
Similarly consider the length of pipe runs for hot water.

Finally, rather than cut back on spec, cut back on size.
Have fun.

sydthebeat

gruby wrote: »

for the sake of getting quotes I think enough would be to :
1. go to environ.ie > building standards> part L to get required U values ( 0.16 for roof, 0.15 for floor with UFH, etc...)
2. google "how to calculate U vsalue", there are many online formulas/ guides for everything and as result you will have the rough required thickness of insulation needed
those figures will be a minimum, go for 30-50% increase as this going to be your house, and you want the average and not the worst case spec

In all due respect, that would be a complete waste of time for both the client and builder.