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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorTriassic
    • CommentTimeAug 28th 2014 edited
     
    I just hate being put on the spot when I'm still trying to get my head around U Values, value for money and the implications of selecting one U Value over another U value.

    So the Timber Frame company called to ask which insulation package I'm interested in. They offer a range of wall and roof U Values staring at 0.24, which I've discounted as being far to poor. So I'm focusing on their better offering of 0.12 or 0.10 for the walls and 0.18 or 0.13 for the roof.

    Starting with the walls - If I got for the 0.12 it will cost me £9,900 and 0.10 will cost me £12,000.

    The roof - If I go for 0.18 it will cost me £4,800 and 0.13 will cost me £5,550. All based on the use of PIR.

    Is it worth the extra for the better u values. Is PIR the way to go, or would the use of other insulation offer better value for money?

    The self build has a floor area of just over 300m2 and the insulation package prices above are supply only, which I would then fit, alternatively I can get it fitted by them at an extra cost.
    • CommentAuthorbarney
    • CommentTimeAug 28th 2014
     
    Which way is the wall thickness proposed - ie smaller internal rooms or bigger house - that has a bearing on efficiency - which can be costed

    From there, and presuming you know the rough shape of what you want, then you want a simple spreadsheet that determines the whole house heat loss ie how much wall of what area and U value, same for roof, floor and doors windows - as you vary the parameters of the wall and roof U values you can then contrast the varying kW loss with the cost of energy and decide what the payback is - ideally by using a simple degree day analysis so you can get a flavor for the annual heat energy used.

    I'd have thought the timber frame company could run the various options through the thermal model for you and give you not just a menu of prices, but a menu of prices with the paybacks

    Regards

    Barney
    • CommentAuthorTriassic
    • CommentTimeAug 28th 2014 edited
     
    I've started to populate my spreadsheet and will do the 'what if' scenarios once I have all the data/areas/sizes I need from the architect.

    I suppose I'm putting the cart before the horse. but I just wanted your thoughts on the use of PIR (as suggested by the TF company) and if anyone had anything could suggest a better option. Also, with one eye on cost, is PIR the best value?
    • CommentAuthorArchmoco
    • CommentTimeAug 28th 2014
     
    PIR will be generally be the most efficient regarding insulating performance and depth.

    Is it a traditional timber frame inner leaf with cavity and brick/block outer? Also is it a standard room in roof truss or a cut Roof

    Are they proposing this in the cavity or timber stud. DIY it is a pain in the a## or at least very time consuming to fit between studs, I would recommend let the guys with experience do it and scrutinise the finished job before the membrane goes on make sure there are no gaps, I believe the guys on site slightly taper the cut to get a snug fit.

    Generally the sheet joints are all foil taped, the 'issue' is this seals the wall and doesn't let the building breathe. Because of this Rockwool, Borax, sheeps wool, hemp have all Been used as they will allow the walls to breathe, but for the same depth of material compared to PIR the 'U' value will be less.
    • CommentAuthorGotanewlife
    • CommentTimeAug 28th 2014 edited
     
    £2850 is the difference: if you have an idea of how long you are going to live there (and it is a long time) and that money isn't already allocated (!!) then I would say spend it - for a start how much will heating cost you in 10 years time - no spreadsheet will tell you that! In short, I would counsel a qualitative decision and save yourself a lot of time number crunching.
    • CommentAuthorEd Davies
    • CommentTimeAug 28th 2014 edited
     
    Posted By: ArchmocoPIR will be generally be the most efficient regarding insulating performance and depth.
    I've added some emphasis. PUR/PIR is great if you're restricted on depth.

    Mineral wool is a lot cheaper in terms of money and embodied energy/CO₂ for a given amount of insulation value. With my small house I've decided on a compromise of a mix of mineral wool and PIR - the major consideration being the depth of window reveals for my relatively small windows.

    With your larger house then maybe full depth mineral wool would make sense. However, that probably results in a structure depth that the kit companies aren't used to. A conundrum.

    I'd agree with Gotanewlife - don't bother with very detailed calculations. See what makes sense using back-of-the-envelope calculations and add a bit of insulation to hedge against energy price inflation.

    If using heating degree-days, don't forget that extra insulation doesn't just decrease the heating bill by U-value × area × degree-days × 24 watt-hours, it also, in effect, decreases the base temperature because it increases the proportional effect of incidental heat gains through windows, from bodies, from appliances, etc.
    • CommentAuthorbarney
    • CommentTimeAug 28th 2014
     
    I've started to populate my spreadsheet and will do the 'what if' scenarios once I have all the data/areas/sizes I need from the architect.


    You don't need a high degree of accuracy at this stage - it's a comparison you are after - so basically all you need is roof area, wall area, % of wall are that's glazed and the GF area - just treat it like a big box as the internal conditions are pretty similar.

    As for predicting future fuel costs, then again all you are looking for is a simple payback - fuel costs are not going to drop over ten years that's for sure

    As above - PIR is almost certainly the most efficient

    Regards

    Barney
  1.  
    I'm not a big fan of rigid insulation within a timber frame panel.

    I know for sure that it is very hard (if not impossible) to cut it in tight so that the panels are fully filled without any gaps at the edges.

    Even if the panels are perfectly filled at the time of installation that's only at one given point in the year. Timber expands and contracts with the seasons, what effect is that going to have? Will a panel that was perfect in the summer have a small air gap at the top or bottom in winter when the timber expands? In the long term will the yearly expansion and contraction lead to crushing of the edges of the insulation boards?

    I've seen PIR applied well in light metal frame buildings where movement isn't a concern but personally I have reservations about its use in timber frame.

    What is your wall build up for the different options? Are steps being taken to address the cold bridging of the studs?

    In my own house I went with mineral wool batts that will expand and contract with the movement in the frame, but there is a price to pay for that in terms of the wall thickness which in my case has an overall thickness of 43.6cm including a total of 36cm of mineral wool giving a u value of 0.095 W/(m²K) . On the ground floor alone that accounts for a loss of 10m² of internal floor space compared to a standard 145mm stud wall on a slab of 150m² overall size.

    I'm surprised that the best that they can offer you on the roof is a u value of 0.13.

    If I am correct you are building 1 1/2 storey over semi basement? So with rooms in the roof you are looking at a considerable portion of your heat loss being via the roof.

    Again there is a price to pay in terms of lost floor area by going for mineral wool over PIR, but my sloping roof supposedly achieves a u value of 0.082 with 500mm of blown mineral wool and I have 800mm of it above the flat ceilings.

    Even with these u values I don't hit the German PHI certification targets due to my choice of 0.9 u value windows.

    No doubt you can build a low energy house with the better of the u values you are being offered but you will still fall considerably short of passive house performance.
    • CommentAuthorTriassic
    • CommentTimeAug 30th 2014 edited
     
    So to answer the question about wall and roof build up .....

    Walls - u value 0.10?

    25mm larch cladding
    25mm battens
    50mm PIR
    Breather membrane
    140mm frame filled with 120mm PIR (questioning the 20mm gap)
    50mm PIR
    25mm battens
    12mm plaster board

    1.5 storey, room in the Roof - u value 0.13?

    State
    Battens
    Breather membrane
    Counter battens
    9mm darling OSB
    140mm trusses filled with 120 mm PIR (again questioning the gap)
    50mm PIR
    Vapour membrane
    25mm batters
    Plaster board

    So I was thinking I could fill the 20mm gap to improve the u values. I'd also like to make sure the insulation was sealed into the messages of the frames, I assume I'd use a low expansion foam for this?

    You comments and suggestions to improve the above build up next welcome.

    One final question, is there an online u value calculator to check the finished value of the above build up?
    • CommentAuthorwoodgnome
    • CommentTimeAug 30th 2014
     
    David Freeborough usually has a good explanation regarding gaps in insulation in the roof construction.
    • CommentAuthorArchmoco
    • CommentTimeAug 30th 2014
     
    Just a small construction point for the larch. The 25mm baton is this a counter batten on a 50x50 with the PIR between? Or is the batten sitting directly on the PIR with fixings through the whole lot to timber frame/sheeting.

    I ask as if you are using 50x50 batten with PIR between just be careful as usually 44x44 or 44x47 and I ended up using 40mm PIR

    The thickness of PIR check with suppliers I ended up having to use 2 layers due to delivery times, two layers is handy for the floor, I had 150 PIR 50mm layer cut between pipes with 100mm over the top. With your roof you might end up with a 40mm&100mm boards or pay extra, 2 layers a pain x2 the work!
    • CommentAuthorTriassic
    • CommentTimeAug 30th 2014
     
    Posted By: woodgnomeDavid Freeborough usually has a good explanation regarding gaps in insulation in the roof construction.
    Thanks for the reminder, I've found David's comments from February and will take them on board
    .
    •  
      CommentAuthorfostertom
    • CommentTimeAug 31st 2014 edited
     
    Between timbers, I agree rigid board insulation is only an option if all edges abutting timber, and all joints between boards, are filled full-depth with squirty foam - laborious, fail-prone and expensive. Otherwise you'll have very numerous straight-through shortcuts for air convection driven by considerable temp difference, and you'll get nowhere near the quoted U value. Even fag-paper thickness open joints are convection channels.

    Cut roll insulation is better - but still hard to get to sit perfectly with just slight compression everywhere and no gaps - the temptation to 'stuff' is great.

    Between timbers, I'd only use blown-in cellulose - Warmcel - or sprayed-in foam-up Icynene, which has very similar properties (e.g. breatheability) and almost as good eco-credentials as Warmcel. Don't believe the bad press about Warmcel slumping - there's good practice ways to absolutely avoid that, which I'll expound if needed.

    Ed is right - mineral wool (incl fibreglass) gives most insulation for the money, albeit at greater thickness. To that, I'd add that similarly, white EPS board or even grey/silver graphited EPS board gives more insulation for the money than any of the foamed insulation boards such as PIR, again albeit at greater thickness. All of these have much better eco-credentials than the foamed board insulations, as well as being very to adequately breatheable, which most of the foamed boards aren't.

    Consider buying a bare timber frame of 6" or 7" or 8" deep members, and cross-battening the studs and rafters externally on site with 3x2 on edge, then blowing the whole 9" 10" or 11" cavity full with Warmcel. Guaranteed to fill every crevice, under permanent slight compression, and the cross battening gives plenty of ledges for the Warmcel to lock around and not slump. Pic attached.

    Cross battening studs and rafters has implications on how you fix wall cladding and/or roof tiling, depending whether you'd be providing an additional stand-off batten anyway; your roof frame could consist of close-spaced lengthwise purlins rather than down-slope rafters, so the cross battening would end up running down-slope if necessary. Note how purlin construction gives great opportunity for overhanging verge.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 31st 2014
     
    • CommentAuthorbarney
    • CommentTimeAug 31st 2014
     
    Polypearl Plus Tom ?

    I've been thinking about this based on something you said a while back actually

    using 4" x 2" I was planning a 3 layer frame (so timber vertical on inner and outer faces and horizontal to seperate them on the middle frame (sort of modified larsen truss idea). That gives a 300mm "void" and the cold points are limited to 2" x 2" squares.

    Then 50mm grey EPS on inner and outer faces all sandwiched in 18mm OSB 3 boards

    Constructed on site rather than as factory "cassette"

    inner skin can the be battened for service voids and PB with a vapour membrane on the OSB

    Outer skin again battened in 3" x 2" and clad - again a membrane on the outer OSB skin

    Fill the lot with blown in EPS beads

    Sensible ?

    Regards


    Barney
    •  
      CommentAuthorfostertom
    • CommentTimeAug 31st 2014 edited
     
    Great, except why 3 layers when 2 will do, only one of which requires a foundation? And why EPS inside and out, when 300mm of blown Warmcel is as much as anyone could want?

    You only need plasterboard on the inside, not needing to be an air barrier, so electrician is free to poke holes in it, no service void needed - OK uprate the cabling a bit, can be pre installed or fished through the Warmcel.

    External OSB power screw/nailed and bubble-glued at all joints as structural sheathing and airtight 'tea cosy' free of need for penetrations. You can use square edge 9 or 11mm Smartply no-added-formaldehyde lo-miles (ferry from Cork) OSB, all joints backed either with a structural member or dryliner's 100 x 0.7mm galv flatstrap and angles, similar to pic attached (from a differently-built job). No timber noggings, minmised timbers degrading the insulation zone. Provides an air barrier robust, cheap, foolproof (except as Mark Twain said, 'fools are so darn ingenious') - no expensive, tricky, fail-prone tapes and membranes.

    The whole thing unobstructedly breatheable.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 31st 2014 edited
     
    •  
      CommentAuthorfostertom
    • CommentTimeAug 31st 2014
     
    • CommentAuthorbarney
    • CommentTimeAug 31st 2014 edited
     
    OK - thanks Tom - to expand a bit, the end walls of the building are planned as dense concrete block inner, 300mm cavity and stone/brick external skin

    There is a further dense concrete block on flat sleeper wall at the mid length of the property

    Dims circa 10m x 8m 2 storey (with skeilings first floor) and a cut roof - again with 300mm of EPS beads and a further 100mm EPS inside and 100mm eps outside before battening and slates (or perhaps a combination of slates and integrated roof PV and/or solar thermal - but that's low on my list)

    The build up above is the front and back of the building

    Basically it looks like a barn - it's being built under 106 notice in a garden

    I've access to a numbe of Schuco AWS 70 units (mis measured for a commercial job) and I like the barn style with the commercial window details - but they are big, including a section that's 4m high and 3.6m wide - so a lot of glass (but DG) - so the idea of the inner and outer 50mm EPS in adition to the 300mm lattice with EPS Bead was to maintain the overall facade U value - ie better walls to compensate for windows - and the 3 layer 4" x 2" was just to maintin a 300mm void as the end wall cavities

    Due to time frames, I'd like to have the fabricated wall and glazing in place and airtight before worrying about the services inside and the cladding outside - was thinking 18mm OSB - I'll take a look at thinner OSB and certainly the strapping

    Not sure what the cladding might be at this point - thinking maybe scaffolding boards run through to create laps and V joints onto 3" a 2" battening and then dyed smokey grey/black

    The masonry end walls are wider than the building width so "wrap around" the timber facade - a sort of buttress style

    So - nice to know that even in GBF land, there is a point where insulation can be overdone :boogie:

    Floor joists run parallel to the facade so don't connect to the timber frame - but it does carry the roof load

    Regards

    Barney
    • CommentAuthorTriassic
    • CommentTimeAug 31st 2014
     
    But warmcell have gone bust, so who supplies it now?
    • CommentAuthorBluemoon
    • CommentTimeSep 2nd 2014
     
    Warmcell is what I was planning to use! When I can get the planners to see things my way.
    • CommentAuthorTriassic
    • CommentTimeSep 2nd 2014
     
    From what I've read the manufacturing plant in Wales went bust and has been bought by another company who will move it to another location. Installers are getting the raw materials from elsewhere.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 2nd 2014
     
    Posted By: TriassicInstallers are getting the raw materials from elsewhere
    That's interesting - it had seemed to be an unhealthy monopoly, 2 or 3 European-name competitors having disappeared - so how could they go bust?
    • CommentAuthorTriassic
    • CommentTimeSep 2nd 2014 edited
     
    Here is the article about Excel going bust http://www.greenbuildingpress.co.uk/article.php?category_id=1&article_id=1878

    In it they talk of competition in their export markets causing the financial difficulty. So who is left, who should you use if you wanted cellulose insulation installing?
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 3rd 2014
     
    Their website seems to make no mention of it, nor does companies house. And the article says that they are moving to a smaller unit.
    So looks like it is still available.
    Maybe some local Welsh business grants have vanished, or there are better ones elsewhere.
  2.  
    I remember speaking to a guy in Ireland who was using a German father and son who were based there and they were very particular about which cellulose they would install citing a huge difference in settlement between brands. They were also very particular about their equipment and how it was used.

    I'll see if I still have some of the details at home later.
    • CommentAuthorTriassic
    • CommentTimeSep 3rd 2014 edited
     
    Posted By: Chris P Baconremember speaking to a guy in Ireland who was using a German father and son who were based there and they were very particular about which cellulose they would install citing a huge difference in settlement between brands.
    Now that's interesting, is there any evidence, research, etc?
    • CommentAuthorTriassic
    • CommentTimeSep 9th 2014 edited
     
    So having discussed the wall build up with the architect he's now suggesting

    25mm larch cladding
    25mm battens
    '50mm PIR'
    Breather membrane
    9mm sheathing layer
    140mm frame filled with Warmcel cellulose insulation
    50mm PIR
    VCm
    25mm battens
    12mm plaster board

    If we use PIR (which I understand to be vapour impermeable) on the outside and inside of the frame, will the building breath, or are we asking for moisture to build up within the frame?
    • CommentAuthorDarylP
    • CommentTimeSep 9th 2014
     
    Triassic, the 50mm PIR on the o/s is relatively vapour impermeable, so the frame will not breathe to the outside.
    With the 50mm PIR on the inside, it will not breathe to the inside either!:confused:
    Does it need to breathe?
    • CommentAuthorTriassic
    • CommentTimeSep 9th 2014 edited
     
    Posted By: DarylPDoes it need to breathe?
    I suppose that the question? Does a timber frame need to breath? I don't know?!!
   
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