Debating All Aspects of Passive Houses - And May the Best Argument Win!
You are not logged in.
Hi
I undertook the training last year to become a Home Energy Rating Assessor under the EECA/ABSA flag.
It strikes me that upgrading the existing fleet of homes in NZ is the best way froward in energy efficiency. What was completely absent from our training is what is considered best practice for each component of a house (eg underfloor) and thus the target we should be aiming to aspire towards. So I'm asking you x-spurts just what can be achieved on a Kiwi timber/weatherboard/corrugated iron house.
Should this be broken into different categories?
Underfloor
Walls
Ceiling
Water heating
Heating
Glazing
Airtightness.
Just how close can one get to Passive without getting silly?
Offline
Hi Sam,
Depends on construction method you are presented with, and the amount of already decided upon work, I'd say. With the usual 90mm cavity, there is only that much insulation to add, without incurring huge extra cost - unless you wanted to re-line the interior or exterior anyway. A reasonable approach to retrofit in my view would be to go for the optimum performance whenever you touch a building element, i.e. re-cladding, re-roofing. More options available for non-timber constructions.
For your categories: airtightness is something to think about whenever you go about doing something with the interior lining; glazing shouldn't be looked at in isolation from frame and edge spacer, unless in the rare occasion when it is reasonably possible to retrofit windows with efficient multipane glazing (usual windows in NZ are neither structurally capable of dealing with the added weight, nor are they in any form airtight to get a good overall window performance). Water heating can be tackled independently from other building work; however, it would pay to thoroughly insulate all pipes, which might be tricky. HRV should be considered once airtightness is sufficient. Heating: should not be necessary any more, once you've dealt with the rest.
Getting a good airtightness concept going and reducing thermal bridges is the black belt of energy efficient retrofit. It has been done, though, with "silly" being in the eye of the beholder, but the cost for getting this 100% right are considerable, unless you have an already gutted house.
Offline
kr I'm trying to work in with the government upgrade initiatives of state (and other) houses. The trouble is that they don't appear to have a target to aim at. We need to develop an understanding of what's possible first and then work backwards to achieve best value in real world situations.
Take underfloor, what would you guys do to a current t&g floored house up on piles.
What would you do to the walls etc.
I have been speaking with the Green party to try and establish guidelines. I have little or no faith in BRANZ or Building Industry groups. I'd like to think you Passivists might be ideal to assist in dissecting the 'average' house and working out best practice.
kr I do tend to agree that re-cladding is the way to go. I have in mind some "Mitre 10 dream home" type competition where two identical houses are renovated, one from the inside (relining) and the other from the outside (recladding) and see how the costs vs benefits stack up. Or has this already been done?
Offline
There is a book from 1984 called "The Superinsulated Retrofit Book" by Brian Marshall and Robert Argue. Whilst not PassivHaus it definitly maps out the key parameters. (The biggest problem with the book is that thermal bridging it not adequately considered and that airtightness is not push as far as we now know is viable. Nonetheless it is an excellent source for ideas and information on the refurb of timber frame homes.)
Mark
Offline
Sorry, there is no one-answer-fits-all ex-state houses. I was involved in >6,000 energy efficiency retrofits in Germany as part of a federal state incentive programme. If money is not an object (and we had those projects, too) you just gut the house and build quasi new. But if economical considerations play a role, a step-by-step programme has to be tailored for each and every house - even when they are identically built. Again: doing energy efficiency upgrades in line with things that need to be done anyway makes most sense in this regard. And to clear up a misunderstanding: I don't think re-cladding is the way to go. What I was saying is: once it comes to re-cladding (because the weatherboards need replacing anyway), this is an opportunity not to be missed to get it right for the next 50 years, and go for the technical optimum.
Few things can be viewed in isolation from renovation circles, if you want to do it economically. The mentioned t&g floor on piles might be one. Here, I would first of all create airtightness (with suitable foils or building papers and sealing tapes fit for the purpose - not many are), then I would figure out if the joists are deep enough to give sufficient space for the insulation required, and if the are not, extend them. Then I would squeeze a blanket type insulation in between the joists, and cover with a suitable weathertightness membrane (depending on wind exposure, topography etc.). Whether or not this is easily done from the outside depends of course on the circumstances; maybe you need to do it from the inside, which would require a different approach.
Offline
Re-cladding is not the way to go. Ok, but insulating walls must involve either re-lining or re-cladding or injecting goo. I'm not a fan of injecting goo. That leaves re-line or re-clad. In my experience the effort required is similar but the re-clad option produces far superior results including sorting out the plumbing, wiring etc far more elegantly than the other.
One area that I have no answer for is an insulation panel to use as a sub-cladding to address thermal bridging and airtightness. I used triple-s board (pinex) on my house, but it's not made anymore. I have not spotted a viable alternative since, have you?
I am a firm believer in a sub cladding/ cavity/ cladding system as it appears to address thermal efficiency and weather-tightness far better than the simple house-wrap then cladding that usually goes on now. To me Batts that are up against breathable house-wrap will not work as effectively as Batts fully enclosed by a sub cladding, am I correct in that assumption?
Offline
Let's now go underfloor..
I reaaly struggle to see how the 'EXPOL' type polystyrene products can be effective. Heat loss underfloor is via radiant loss and air movement, yes? Don't those ribs on the top of the Expol create the air space that the breeze needs to carry heat way?
My thoughts are for insulated (bubble wrap) type foil fitted under the joists taped etc to create a stiil air zone within the joist space, just as you suggested. The foil reflects back the radiant heat loss and the air-tightness stops the stripping of heat away via drafts. Further the insulation of the foil reduces the thermal gradient of the inner foil surface and moves the dew point (down) out of that area = no condensation or rising damp. So far so good. What I query is if there is then further to be gained by filling that (now enclosed) inter-joist space up with another product? Is it possible that it might make matters worse, or at least not better enough to warrant the cost. If that fill should sag down to touch the foil surface won't it then negate any reflective/radiant insulation and effectively turn the foil into a conductor? So if I'm right, does that make products like Batts Cozy Floor (foil laminated onto Batts) flawed as well?
Offline
Back to re-cladding: sure, once you are at this stage, you have a lot more options to get it right - but if the cladding still has decades of use in it, it is an economical waste to re-clad.
Injection: there are some really good products on the market in Europe (silicate granules, perlite, mineral wool granules), that are fit for the job. I have grave concerns, both technical and environmentally regarding foams for this. Thermal bridges remain an issue, of course, particularly with the very narrow cavities you get in line with NZS 3604.
Once you re-clad, sub-cladding with an insulation product is a good idea, but again: while there are a few good options available in Europe (eg hydrophobic softwood panels or MDF) here options are pretty much non-existent. And yes: you improve the thermal bridge situation significantly by putting an insulation layer externally of the battens.
I share concerns regarding EXPOL type insulation, but insulated foil does not make much sense to me either. Effects of radiant reflection (for there to be any, the foil would need to be shiny in the first place) are grossly overestimated in NZ. There are some minor (compared with other thermal processes) effects, but only as long as the surface stays shiny, eg free of dust and corrosion. How likely is that? Leave the insulation to purpose made materials i.e. materials with a very low thermal conductivity. The purpose of the foil or building paper that I suggested is purely to achieve airtightness inwards of the insulation layer. Note: this foil or building paper needs to be immediately under the t&g to have this effect - not under the joists. Foil under the joists has negligible effects as it neither creates a still air cavity (the t&g layer is not airtight, and by walking on it, you get a pump effect; but even if there was a still air cavity the effects are minor) nor does the radiant reflection work (at least not for long, and even as long as it works it is insufficient). You have to fill the space between the joists - but that is not enough: depending on the type of underfloor cavity, you might need additional measures externally of the insulation layer to prevent windwashing and moisture ingress into it. Foil laminated batts were prevalent in Europe in the 70s and 80s. Luckily, they are all but vanished from the market there by now, as there are some problems associated with them, particularly regarding airtightness. I would not use them. Cozy Floor: as Pink Batts are much more fluffy (markedly lower density) than glass wool products in Europe, I have concerns regarding sagging, that I would discuss with the manufacturer to see if they can put those concerns to rest. Bradford Gold is denser, some other products are, too.
Offline
kr this is getting a bit lonely just you and me, we need others to weigh in..
So, you see now why I started this thread. The government is prancing around throwing yours and my money at a problem without having a correct solution at hand.
You say it is an economical waste to re-clad, is it though? I'm sure I don't know the answer but who does esp when you calculate the saving in electrical grid infrastructure, health costs etc associated with a snug home, or thousands of them. Has this been done?
Do you have a link to an example of a hydrophobic softwood panel?
Do you know of a product to caulk the gaps in the t&g flooring?
I do agree that the foil will get dusty.
I have considered Pinex under the joists with foam to seal any gaps, but haven't done it.
I guess I reach the point where I think government should say to all the underfloor insulation providers "Not good enough, go away and come back with the correct product"
While we are groveling under houses.. why, in the old days did they put houses so low to the ground? No wonder we dave dampness issues. It makes it mighty hard to insulate!
Windwashing... just how much subfloor ventilation is correct? Enough to vent moist air but still keep wind speeds low, how many air changes per day? I suspect current practice over-ventilates?
Offline
Economical waste: I was thinking private economy here, not big picture. Big picture might be a different case altogether, but very hard to seriously calculate.
Softwood: Check http://www.glunz.de/flycms/Konstruktive … 35458.html
http://www.egger.de/de-deu/egger-de-pro … n_7910.htm
(German, but with pictures)
http://www.steico.com/ (yippee, some English pages); maybe Mark can chip in with some British examples?
Caulking t&g: just too may gaps here to caulk, and uncertainty re movement, so wouldn't do it and use foil/paper instead. Theoretically, you could use SIGA tapes, but at a cost: www siga.ch
While we're at it: the government should say 'not good enough' to quite a few manufacturers in the business of energy efficiency. Just try to get some solid building physics data of any insulation product in NZ: it"s a nightmare!
In the olden days people did what they knew from building in the countries of origin, and made do with what materials they could get a hold of. I don't blame them. Today, we should know better, and should have better materials and construction methods available - that's the real shame.
Subfloor ventilation: in Scandinavia, they pretty much stopped doing that at all, cause they discovered that, yes, you get rid of some moisture during winter, but you import a moisture problem during summer in a ventilated subfloor. In summer, warm, moist exterior air will condensate on the cold subfloor surfaces when it gets there. The amount of imported water can be significant, as warm summer air can store a lot of water. It's not easy to get a good balance here. WUFI would be the programme to use to get an idea of what is going on for individual projects in individual climates.
Windwashing is another topic altogether, though. In moderately ventilated subfloor cavities this might not be a huge problem, but the more wind you allow in, the higher the risk that you get circulation around your insulation layer, rendering it pretty much useless. As Mark just gave a talk on these effects in Frankfurt, I am sure he can expand on that. See: I am attempting to get other people in on the discussion!
Offline
How about we jump into the ceiling now...
Timber framed /corrugated iron. Batts between joists then Batts rolled out across the joists to R5, is there much to be gained by going to a higher rating? I'm lead to believe there isn't.
As per the subfloor just how much ventilation should the attic space have? I have been taught that it's important to have plenty of air movement up there, but what do the passivists have to say?
Offline
I assume the ceiling forms the thermal envelope here (as opposed to pitched/cathedral roof)?
Again, I would start with an airtightness barrier as the most interior layer. What happens next would depend on the uses of the roof space, if there are any. If roof is used as storage, I need a rigid surface with some load bearing capacity. In this case it would be interesting to know how you get up there, as the access way would have to form part of the thermal envelope. In a ventilated roof, a wind barrier would again be needed (the rigid surface could double as one).
As a general approach, I would always go for the maximum insulation within my budget, whenever I insulate at all. The reason for this: insulation itself is rather cheap - labour is the largest chunk of the cost. While it is true that the first centimeter of insulation is the most effective, added insulation has always added value, not just in saving energy, but also in increasing comfort. Therefore a do-it-once-do-it-right approach is the most sensible.
Ventilation: condensation is a concern again. Due to radiance to the sky, the iron or tiles can be significantly colder than exterior air in clear nights. Thus, if the roof is ventilated, condensation - this time in winter and summer - is a concern again. This has to be weighed against the possibility to ventilate off excess moisture at other times. Again, it depends on the individual situation what the smartest approach to ventilation might be. In any case, this needs to be well reasoned or better calculated.
Offline