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Author Topic: Meeting building regs on insulation for single storey roof/ceiling  (Read 6270 times)
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« on: May 13, 2014, 10:20:30 AM »

Hello folks. My friend Rob is building an extension. It's a single storey L shaped 'wrap-a-round' on the back of the house, and partly down the side.

He's a little out of date with the current building regs and products for meeting insulation levels. Can you help?

Here's the issue. The ceiling will be flat, and so plenty of room for insulation. However, on the back part, he is fitting 2 Velux, and rather than create skylight tunnels (is there a proper name for this?) he wants to recess the roof from either side of the Velux, and the ~2m between, by working to the sloped roof.

When he re-built our kitchen, we had a Velux added, and rather than a tunnel, he came up with this idea:-



Tried to take a photo of the finished product, but sun is blasting through, and camera going nuts. But hopefully you can see the idea. He and his wife are taken with the look. For his house, the flat roof/tunnel would reach the outer wall, whereas ours meet halfway.

Now to the problem. He has used 5inch joists, and he (and I) assumed no problem meeting regs, but has now discovered that 4 or 5 inches of 'normal' PIR might not do it. I've suggested he pop to the local Minister depot, who are really helpful, and ask for suggestions/products. But belt and braces, said I'd ask on here too.

I believe he has to meet a U value of 0.25, is that correct, is that the same as 0.25W/m2? Apologies for not knowing/understanding more.

Any suggestions on products or combinations that would do it? He doesn't mind adding insulated plasterboard around the Velux's but would like to keep it as flush as possible (ie minimal tunnel). Also how are combinations of products, such as space blanket plus PIR installed, gaps to felt etc etc.

Please, any advice on a level that I'll understand, and be able to pass on ...... without having to bluff (too much).

Thanks.

Mart.
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
ianh64
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« Reply #1 on: May 13, 2014, 10:35:37 AM »

Velux do an insulation collar in addition to the flashing kit. Obviously, for anything other than a basic Velux fit of smaller sized units, building control will want to see the calcs for roof structure.

I've got one for each my my two Velux, still sitting in my garage as I cannot find anyone willing to fit and build the tunnel/remodel ceiling and joists. If anyone in N.SurreyBerks/Hants border willing to come and quote, please PM me.
« Last Edit: May 13, 2014, 10:47:40 AM by ianh64 » Logged
brackwell
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« Reply #2 on: May 13, 2014, 10:56:07 AM »

This suggests quite a few will do this  http://www.broxbourne.gov.uk/PDF/TECH_NOTE_10_2010.PDF

Ken
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A.L.
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« Reply #3 on: May 13, 2014, 12:01:22 PM »

hello,

Quote
I believe he has to meet a U value of 0.25, is that correct, is that the same as 0.25W/m2? Apologies for not knowing/understanding more.

- not fully familiar with English regs, but I think he has to achieve 0.18W/m2.K - see page 17 of doc (or 19 of pdf)
http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_L1B_2011.pdf

- on this basis 125x50mm rafters @ 600mm centres would require a further 25mm of PIR below rafters to just meet 0.18
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« Reply #4 on: May 13, 2014, 01:27:58 PM »

hello,

Quote
I believe he has to meet a U value of 0.25, is that correct, is that the same as 0.25W/m2? Apologies for not knowing/understanding more.

- not fully familiar with English regs, but I think he has to achieve 0.18W/m2.K - see page 17 of doc (or 19 of pdf)
http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_L1B_2011.pdf

- on this basis 125x50mm rafters @ 600mm centres would require a further 25mm of PIR below rafters to just meet 0.18

That's interesting. It does seem to suggest 0.18W/m. Though I don't pretend to fully understand it.

One thing I did notice was that it said:

Quote
2. Area-weighted average values.

Does that simply mean that if he 'over' insulates the rest of the roof, that it can be balanced out? Rough guess, I'd suspect the Velux + space + Velux adds up to about 4m out of a total roof length of approx 11m (8m across the back + 3m down the side). Taking this average question even further, will he also need to include the U value of the Velux's (Veli?) in said average?


Cheers Ken, looking at that, I suspect he'll need a bit of insulated plasterboard to meet regs, unless my question (above) is right.

Mart.
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A.L.
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« Reply #5 on: May 14, 2014, 04:53:38 PM »

hello again,

-apologies for slightly slow reply,

Quote
Taking this average question even further, will he also need to include the U value of the Velux's (Veli?) in said average?

- no, these are windows  Grin and need not be included

Quote
Does that simply mean that if he 'over' insulates the rest of the roof, that it can be balanced out?
- yes, but be careful, due to the diminishing returns of insulation thickness adding 1m2x50mm will not compensate for removing 1m2x50mm and in a critical situation like this could/will be insufficient. The average heatloss W/m2.K must be 0.18 or less.
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« Reply #6 on: May 15, 2014, 01:27:56 AM »

It's a really good idea to have some continuous insulation over/under the joists anyway as otherwise they are big thermal bridges. Similarly you need careful design to stop the frames round veluxes being massive thermal bridges. The feeble 20mm foam insulation collars fakro/velux sell help a bit but not much. 
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« Reply #7 on: May 15, 2014, 07:16:46 AM »

Thanks folks. I'm finding this interesting. And A.L., yes that makes sense, the diminishing returns on extra insulation won't balance 1 to 1 with 'missing' insulation. So if he goes down that route, he'll need to carefully consider the additional gains, and the larger area (on which it resides) and presumably clarify with building regs inspector before jumping in.

Personal question, and apologies if it's a bit silly, but I'd have thought (ignorantly) that a 125mm joist (where a 100mm would have been more than adequate) would have allowed plenty of space for acceptable levels of PIR insulation. Am I right to now think I'm very wrong IYSWIM?

This leads on to my extension plans. I'm planning a utility/storage room (garage without a garage door) on the side of the house. It'll be approx 6.5m by 2.3m, with the roof running side to side. So the joists will only be about 2.5m long. I've assumed that even though unheated, I'll still have to meet building regs on insulation, in case its use ever changes. So presumably I should also consider larger joists to allow adequate insulation. Not actually a problem, as I was going to suggest oversized joists, perhaps 150 to 175mm so that I could add brackets to store wood, ladders etc etc anyway. But hadn't considered that insulation may be an issue, and hadn't planned on any ceiling, just exposed joists.

Mart.
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brackwell
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« Reply #8 on: May 15, 2014, 08:09:11 AM »

Mart,

The cheapest and most effective way for your friend is 25mm above and below and fill the gap with 100mm fluffy stuff as it is only preventing convection currents between the 2 surfaces. 

If your space is unheated and not habitable then its like a shed/garage ie no insulation.  Your bigger problem could be convincing them that is what it is.  Do you need planning permission for a garage/shed subject to positioning these days?

Ken
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A.L.
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« Reply #9 on: May 15, 2014, 10:25:29 AM »

hello again,

Personal question, and apologies if it's a bit silly, but I'd have thought (ignorantly) that a 125mm joist (where a 100mm would have been more than adequate) would have allowed plenty of space for acceptable levels of PIR insulation. Am I right to now think I'm very wrong IYSWIM?

- With a bit of luck you should see below the build-up for 125mm joists with PIR. I have added plasterboard as this will meet fire regs. Anything on the cold side of this is likely to be fully ventilated and will not add to the overall thermal resistance.

- 100mm Fibreglass/Mineral wool between joists with additional 25mm PIR on cold side will not achieve 0.18

Quote
This leads on to my extension plans.
- Assuming there is a door direct from house to extension this looks like a room to me. Even if its not, being attached to house I think you would need to cover any oil-based insulation to meet fire regs.


* Mart.jpg (98.13 KB, 645x400 - viewed 1404 times.)
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M
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« Reply #10 on: May 15, 2014, 10:37:58 AM »

Mart,

The cheapest and most effective way for your friend is 25mm above and below and fill the gap with 100mm fluffy stuff as it is only preventing convection currents between the 2 surfaces. 

Very interesting. I've always assumed that the 'insulation' so to speak is the air, but needs to be prevented from moving. So the lighter the insulation the better. That made me wonder if the fluffy stuff was a cheap (but acceptable) alternative to more expensive PIR stuff. As you can tell, I'm interested in the theories, but little knowledge on the technicalities. Will pass on comments and suggest he discuss this with the buildings regs guy.

If your space is unheated and not habitable then its like a shed/garage ie no insulation.  Your bigger problem could be convincing them that is what it is.  Do you need planning permission for a garage/shed subject to positioning these days?

Ken

The space will be unheated, but attached to the side of the house, going over the side driveway. No plans to heat it, and as it's on the NNE wall, I assume it add a tiny bit of insulation (poor choice of words) to the existing house, simply by reducing the amount of air movement on that section of downstairs wall. A bit like our unheated ESE conservatory acts as a buffer between living room temps and outdoor temps, but also has lots of solar gain.

Planning permission. If unattached, no planning subject to size/rules/etc but this is attached. However, in Wales, last year the planning regs changed at the end of September, and side extensions became permitted development, even if within 3m of the boundary. In our case the entire driveway is within 3m!

It does remain subject to a few rules to remain PD, less than 25% of total perimeter, 4m or less at property wall, 3m or less at boundary. Worked out well, as i was putting a planning application together, when Wifey was told by a mutual friend working on the planning portal, to watch this space.

Also, just for those as paranoid as me, when I spoke to the building regs team to arrange registration, I did ask them if they'd mind checking the planning rules, and they put me through to a helpful planning guy in Carddiff Council who ran through the new rules and confirmed it was PD ..... if we stuck to the rules.

I'm happy to comply with all insulation rules, but my only concern is that a well insulated, sealed box with no heating may suffer from some condensation problems. Not sure if I'm making this up?

Mart.
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brackwell
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« Reply #11 on: May 15, 2014, 05:34:21 PM »

Mart,

Good news about the PD but building regs is something else. From building regs partL2A
  "the exemption from the energy efficiency
provisions for extensions consisting of a
conservatory or porch is amended to grant
the exemption only where the existing walls,
windows or doors are retained, or replaced
if removed, and where the heating system
of the building is not extended into the
conservatory or porch"

Your point about condensation?  If water vapour is being created in this space and there is no ventilation from the outside then obviously you will get condensation which you need to address.   If at building inspector stage no water vapour is or will be created (like a garage) then i guess there will be no restrictions.  Just ask the guys.  But whatever you do need ventilation. The insulation changes the heating bill.

Ken
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« Reply #12 on: May 27, 2014, 02:32:05 PM »

Had a fun morning, too silly to start a new thread, but it was at my friend Rob's house, getting the concrete floor poured.

He (and his son's) are no strangers to hard graft, but they were going to barrow 5m3 of concrete from the front, into the back, via a steep driveway. I threw a slight spanner in the works, and asked if it was worth the effort, and mentioned hiring a pump truck. Rob came round to the idea since access was tight, he'd need to hire extra muscle, and pay for the concrete truck to hang round longer.

Oh boy ......... hopefully I'll scrounge some photo's!

I went round to watch. We all expected a medium sized vehicle, with rubber sections of pipe, or perhaps a roll out smaller pipe. Nope, that's not what turned up. What we got was a full size rigid pipe commercial scale jobby. It had 5 lengths of hydraulic booms, before adding any flexible sections. The driver dodged the folded booms around and under all the street cables, before unfolding them, and going clean over the house, and in through the back door.

To say I was in my element would be an understatement. What a fantastic piece of kit, even the stabilisers impressed me, the front ones came out at an angle, and went on and on, but the back ones were actually the rear sides of the truck, and unfolded like wings.

How would the world cope without hydraulics?

Still got a smile on my face, just need to raise the 300,000+ to buy one now (Rob's son wants a digger, and Wifey wants a road roller) it's quite addictive.

Mart.
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« Reply #13 on: May 27, 2014, 02:52:33 PM »

Photos?
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« Reply #14 on: May 27, 2014, 09:24:20 PM »

Got a few pics taken by Wifey on her phone, but impossible to show the size of the boom. However, have asked friend for a pic he took from down the road, showing the boom going clean over the house.

For now, here's a quick snap of the truck, showing the first section of the boom, and the start of the 2nd (3rd, 4th and 5th out of camera view). Check out the size of the swivel base and those stabilisers, and the cables everywhere.



Quick test - does anyone on here know how they clean out the steel pipe after pumping has finished? I was shocked at the simplicity of the solution.

Mart.
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