MBC Cellulose/PIR?

[Visti]

I'm looking for the advice from those who've gone with MBC for their builds with regards to the insulation that was chosen and how you feel it is performing?

 

We're undecided between MBC's options where the U value is 0.15 W/m2k or better (there is a condition of a maximum of 0.15, so that's the minimum spec we can go with. The goal is to have a balance between performance and cost, so a passive standard isn't on our set of objectives. However, we are mainly concerned with several other factors:

• Longjevity
• Sound Insulation
• Air tightness

 

Cellulose appears to have the advantage in all three areas over mineral wool and PIR from the reading we've done. PIR appears to suffer from shrinkage, off-gassing (low u-value gases leaking, reducing the performance of the insulation overall) and doesn't appear as foolproof to install (inaccurately cut and fitted they leave gaps).

 

The main disadvantage is the cost of the cellulose option at+£10k on-top of our initial option of the U=0.15 mineral wool spec.

 

Any advice / experience would be really helpful! Thanks

 

Mineral Wool (MBC Upgrade to U=0.15)

 

PIR (MBC Upgrade to U=0.11)

 

Cellulose (MBC Passive Standard)

 

 

 

Edited November 2, 2017 by Visti

[Jeremy Harris]

I can only comment on the MBC twin stud, filled with cellulose.  The performance is very good, in that the insulation value is pretty good and the decrement delay is pretty long, but the most noticeable effect is the soundproofing.  The house is very quiet inside, and acoustically pretty "dead", in that the reverberation time, even in our large, 6m high, entrance hall.  The result is that you can't hear what's going on outside at all, plus any sounds created inside the house seem to be absorbed.  We hadn't really expected this, but it's something that several visitors have mentioned, with comments ranging from "it feels snug", to being surprised at the noise (we're in a very rural area) when a door or window is opened.

 

I'm really glad we opted for the cellulose fill, as it seems to have so many advantages over the other options.

[dogman]

Like JSH i can only comment on the twin stud, although our last house was a SIP build.

 

We were and to some extent still are a fan of SIPS but having used MBC twin stud for the latest build i am glad we did. A lot is to do with MBC attitude and attention to detail but there are some aspects that are better in my opinion.

 

The foundation package and the lack of cold bridging are a the biggest advantage.. The studs inside the sips and other build methods are a cold bridge and the  need to add insulation on the inner skin adds problems such as fixing it to the frame 

 

As JSH mentioned we found that the whole feeling of the house changed when the cellulose was pumped in and it is some much quieter than the sip house.

 

As for performance i cannot comment as we are still at first fix stage. 

[Ferdinand]

16 hours ago, Visti said:

there is a condition of a maximum of 0.15, so that's the minimum spec we can go with

 

OT, but this interests me. How did that happen?

 

Thermal performance is not a Planning matter, AIUI. 

[ProDave]

3 hours ago, Ferdinand said:

 

OT, but this interests me. How did that happen?

 

Thermal performance is not a Planning matter, AIUI. 

I think that is a condition imposed on all the Graven hill plots. Not so much a planning issue but a condition of sale.

[A_L]

20 hours ago, Visti said:

 

We're undecided between MBC's options where the U value is 0.15 W/m2k or better (there is a condition of a maximum of 0.15, so that's the minimum spec we can go with.

 

 

- Would there be any significance in the fact that the maximum allowable under PH is U=0.15?.

[Dudda]

If money wasn’t an issue (which is never the case) I’d probably go with the cellulose. To be fair in you’re first option where you’ve Frametherm between the timbers, this is a mineral wool which will be tightly fitted between the joints. It’s also good at sound absorption (not as good as 300mm of cellulose but that’s a lot thicker and more expensive). The PIR that’s put over the wall hasn’t many joints as it’s placed over the whole wall and not cut between all the timbers. The second option of the 0.11 u-value where the PIR is cut between the timbers I’d be more worried about as that’s a lot of cutting with a lot of potential gaps. PIR is getting expensive and has crept up in price a huge amount over the last 12-18 months. A lot of the additional cost in the cellulose option is the additional timber. A compromise could be option one but with 70mm PIR insulation internally instead of 50mm which would reduce you’re u-value slightly while still having a low cost and the advantage of the sound reduction of the mineral wool. PIR doesn’t really do sound reduction like the cellulose or mineral wool. Of course you could always look at using the blue acoustic plasterboard internally on the external walls instead of the standard grey. This would really help with the sound if this is a concern and might be a more cost effective option.

Sorry as I’ve kinda increased the options rather than reducing them.

[ProDave]

I was originally having blown in insulation in my 190mm frame, until I found out the cost, and you need a man with the machine to do it.  I changed for the frametherm instead, it gave the same U value and was half the cost, and was a DIY job to fit it.

 

190mm frame with Frametherm 35, 100mm wood fibre external insulation then render, OSB, service void then plasterboard inside gives a U value of 0.14

 

[Calvinmiddle]

I have gone with the 140 mineral wool between the studs and 50 PIR in front - so the first option.

my issues was the same as your in that the cost to the cellulose was hard to justify.

This buildup makes a pretty sound deadening house as well, our house is a bit echoing inside but I think that is more to the fact we have open plan and have tiled floors more than anything to do with the walls.

One think you should do is look at the floor wall interface between the two wall types as I remember having issues with my cladding as the 1st option doesn't overhang the EPS of the foundations and I had to add cross battens and a tricky profile to prevent water ingress.

Can you post the wall floor interface for the 3 options as well?  That might help make your decision I think.

[Visti]

Thanks all for the input though unfortunately the matter is hardly settled! We're dead keen on cellulose following all the feedback but we've just had a quantity surveyor estimate a whopping £400k for a 184m² build, a good £150k over our original estimate of £250k (~£1400-1500 /m²). Hence the need to explore cost cutting options. I'll let you know which route we take following some alternative cost models!

 

On 10/24/2017 at 11:43, Ferdinand said:

 

OT, but this interests me. How did that happen? Thermal performance is not a Planning matter, AIUI. 

 

Correct, it isn't planning; this is a requirement from Cherwell District Council on the plots being sold at Graven Hill as ProDave pointed out. It doesn't affect us as we're keen on good insulation anyway!

 

On 10/24/2017 at 16:36, Dudda said:

...look at using the blue acoustic plasterboard internally on the external walls instead of the standard grey. This would really help with the sound if this is a concern and might be a more cost effective option.

 

Given the £10k difference between the two options, the blue acoustic plasterboard may be a far more cost effective option to keep the sound levels down. Given how much we're looking to shave off the above cost estimate we'll be seriously looking into that.

 

On 10/24/2017 at 17:01, ProDave said:

I was originally having blown in insulation in my 190mm frame, until I found out the cost, and you need a man with the machine to do it.  I changed for the frametherm instead, it gave the same U value and was half the cost, and was a DIY job to fit it. 190mm frame with Frametherm 35, 100mm wood fibre external insulation then render, OSB, service void then plasterboard inside gives a U value of 0.14

 

Thanks for the spec ProDave, we'll look into that as an option as the bare frame with no insulation is only £43k, shaving £20k off the MBC's installation of the mineral wool spec and £30k off the cellulose spec. Obviously the raw materials will cost, but the DIY element would help us retain some of those savings.

[ProDave]

2 minutes ago, Visti said:

Thanks for the spec ProDave, we'll look into that as an option as the bare frame with no insulation is only £43k, shaving £20k off the MBC's installation of the mineral wool spec and £30k off the cellulose spec. Obviously the raw materials will cost, but the DIY element would help us retain some of those savings.

Wow those costs seem high. I guess labour is the big cost?

 

I know my house is smaller at about 150 square metres, but in total my insulation for floor, walls and roof cost under £3K. You will probably want more than me (even allowing for the larger size of house) as part of my insulation is the wood fibre outer layer. I would be very very surprised if your total insulation materials cost exceeded about £7K

 

DIY labour is the biggest input you can have to keep costs down.  I estimate I will have saved anything up to £50K by doing so much of the work myself. But the build is a LOT slower as a result.

[Visti]

Labour and margin I suppose. They're still cheaper than some of the other quotes we've had by far.

 

We don't have the luxury of a lot of time given the 2 year limit to finish the house, and the extra spend to finish quickly may pay off given the £1500 in rent we're forking out until we do.... a delay of 4-5 months doing it ourselves could erode those savings entirely. 

[Ferdinand]

8 minutes ago, Visti said:

finish the house

 

That phrase could have a multitude of meanings. Do you have a definition?

[Visti]

4 minutes ago, Ferdinand said:

That phrase could have a multitude of meanings. Do you have a definition?

 

Not yet, we've asked for clarification as to exactly what needs to be in place for the structural warranty to be signed off and the build considered complete by the Graven Hill team. Once we have that we'll prioritize those activities to move in asap. Once in, we have the luxury of doing DIY on areas where we possibly can. 

[Flyingbartman]

I was very interested in reading this topic as we are doing the exact same exercise. My architect planned for 140mm frametherm 32 between studs and 25mm PIR over the studs followed by 15mm fireboard.

 

I looked into blown cellulose insulation and received a quote for just over 100/m3. The best price I can find for the frametherm 32 is about 93/m3 so for me it is an easy choice as the cellulose is an installed price. It wouldn't even be worth doing the frametherm as a DIY job.

 

Hence I find it interesting to read most people opt for mineral wool due to the cost. Our house is on the large side at 490m2 which may make a difference, however I wouldn't imagine it would make that big a difference.

 

My plan now is for 140mm cellulose between studs with 50mm PIR over the studs taped to form a VCL. On top of this would be a 25mm or 38mm service void finished with 15mm fireboard giving us a U-value of 0.16.

 

Any thoughts would be appreciated.

 

[Ian]

11 minutes ago, Flyingbartman said:

I was very interested in reading this topic as we are doing the exact same exercise. My architect planned for 140mm frametherm 32 between studs and 25mm PIR over the studs followed by 15mm fireboard.

 

I looked into blown cellulose insulation and received a quote for just over 100/m3. The best price I can find for the frametherm 32 is about 93/m3 so for me it is an easy choice as the cellulose is an installed price. It wouldn't even be worth doing the frametherm as a DIY job.

 

Hence I find it interesting to read most people opt for mineral wool due to the cost. Our house is on the large side at 490m2 which may make a difference, however I wouldn't imagine it would make that big a difference.

 

My plan now is for 140mm cellulose between studs with 50mm PIR over the studs taped to form a VCL. On top of this would be a 25mm or 38mm service void finished with 15mm fireboard giving us a U-value of 0.16.

 

Any thoughts would be appreciated.

 

Won't you need an extra layer of OSB or plywood with the blown cellulose option? 

 

 

[ProDave]

Interesting. When I did the comparison, well over a year ago, Frametherm was half the price of celulose. Perhaps the installers that blow it in charge a lot  more up here?

[Bitpipe]

4 minutes ago, Ian said:

Won't you need an extra layer of OSB or plywood with the blown cellulose option? 

 

 

Most of the airtightness layer in our MBC build is a special green faced 12.5mm OSB, however I believe that up until then they were stapling the yellow airtightness fabric to the inner wall studs with the service void battens laid on-top - this is the arrangement we have in our loft.

 

The advantage of the fabric is that you can see how tightly the warmtherm is packed - it really pillows out between the joists.

[Jeremy Harris]

I think installation is where much of the cost lies with cellulose.  The machine is pretty expensive and it needs at least three people to do the job reasonably well and quickly - feeding and breaking up compressed bales into the hopper really needs two guys, if the blowing guy is working flat out.

 

We have 300mm of cellulose in the walls and 400mm in the roof and are pleased with the outcome.  Not only is the thermal insulation good, but it has a high decrement delay and it works as very effective sound insulation, too,

 

Like @Bitpipe, our roof insulation is just blown into the space between the outer sarking boards and the inner Intello membrane.

Edited December 4, 2017 by JSHarris

[Ian]

2 minutes ago, Bitpipe said:

Most of the airtightness layer in our MBC build is a special green faced 12.5mm OSB, however I believe that up until then they were stapling the yellow airtightness fabric to the inner wall studs with the service void battens laid on-top - this is the arrangement we have in our loft.

 

The advantage of the fabric is that you can see how tightly the warmtherm is packed - it really pillows out between the joists.

Thanks for that - I've never used blown cellulose before in walls and assumed it would need something more solid than just a membrane to retain it.

[Bitpipe]

Just now, Ian said:

Thanks for that - I've never used blown cellulose before in walls and assumed it would need something more solid than just a membrane to retain it.

 

I think @HerbJ build used the yellow material, we were done about 6 weeks apart.

 

I only know I was one of the first to get the green OSB as the firm that makes it came to site with MBC to see if in-situ and take photos for their brochure.

 

The yellow fabric is pretty heavy duty but can tear if caught with a sharp edge - I poked a few holes in the loft while boarding out the eaves floor for storage. Easily repaired with spare airtightness tape and the insulation was not going anywhere - it was packed solid.

 

Other advantage of the green OSB is that you can nail or screw into it without compromising the airtightness (providing the fixing stays in place) plus I assume it's much quicker to install.

 

[Jeremy Harris]

31 minutes ago, Bitpipe said:

 

I think @HerbJ build used the yellow material, we were done about 6 weeks apart.

 

I only know I was one of the first to get the green OSB as the firm that makes it came to site with MBC to see if in-situ and take photos for their brochure.

 

The yellow fabric is pretty heavy duty but can tear if caught with a sharp edge - I poked a few holes in the loft while boarding out the eaves floor for storage. Easily repaired with spare airtightness tape and the insulation was not going anywhere - it was packed solid.

 

Other advantage of the green OSB is that you can nail or screw into it without compromising the airtightness (providing the fixing stays in place) plus I assume it's much quicker to install.

 

 

 

AFAIK, Greg Mook's and our builds were both a fair bit before Herb J, as I think Herb came to look at our build before his started.  We have the green board as the VCL, but not the bright green stuff they are using now, a darker green stuff that is some sort of coated chipboard, about 12mm thick.  I have a feeling that it's Spano Durelis, or something very similar,a s it looks identical to it.

 

I think the switch to trying just a membrane on the walls was after our build, and have a feeling that they switched back to using a vapour tight board because it was a lot quicker to fit.

[IanR]

2 hours ago, Flyingbartman said:

Hence I find it interesting to read most people opt for mineral wool due to the cost.

 

I'm also struggling to see the logic behind the price premium for Cellulose. Is the only difference in the quotes the insulation type, or does the Cellulose quote include a different frame technology, ie. twin-stud over traditional.

 

We needed over 200m³ of Cellulose and the installed price was under £15K. It worked out at around £73/m³

[IanR]

On 10/23/2017 at 19:36, Visti said:

there is a condition of a maximum of 0.15, so that's the minimum spec we can go with.

 

How is that condition worded?

 

The U Values being quoted in the images you've supplied are for a theoretical wall section with studs at their standard (300mm/400mm/600mm) centres. With the extra timber that will be needed within the walls around window and door openings or other structural elements such as supporting a ridge beam etc. the actual average U Value will be higher.

 

Depending on the wording of the condition, you may need to go for a wall build up that provides a theoretically higher U value, such that the actual U Value meets the condition.

[Visti]

7 hours ago, IanR said:

 

I'm also struggling to see the logic behind the price premium for Cellulose. Is the only difference in the quotes the insulation type, or does the Cellulose quote include a different frame technology, ie. twin-stud over traditional.

 

I suspect a good deal of the extra cost with cellulose is two fold: the cost of labour in the installation (already mentioned) and the the twin stud frame required.

 

6 hours ago, IanR said:

 

How is that condition worded?

 

The U Values being quoted in the images you've supplied are for a theoretical wall section with studs at their standard (300mm/400mm/600mm) centres. With the extra timber that will be needed within the walls around window and door openings or other structural elements such as supporting a ridge beam etc. the actual average U Value will be higher.

 

Depending on the wording of the condition, you may need to go for a wall build up that provides a theoretically higher U value, such that the actual U Value meets the condition.

 

You're right there @IanR, that's for the whole wall but I can double check when I get back from germany. We'll be adding not much more to the wall. A single layer of fermacell internally and vertical timber on counterbattens outside for cladding, so I'll have to do the calcs for these. It's another reason why we opted for cellulose at 0.12, gives us some leeway!