IanR

Is it a standard build up including the Kingspan K12? This seems to go against the advice from Knauf. From Knauf's timber frame document: Bold format added by me Since the K12 is vapour impermeable, it does not follow this guidance. Might be worth taking advantage of the offer of condensation risk analysis. I have a Touchwood frame, and their standard build up is (inside-to-out): Foil backed plasterboard (VCL) 300mm/350mm JJ I-Joist with Warmcel Eggers DHF Fibreboard (Airtight layer) Breather membrane

Here's a good reference http://www.users.waitrose.com/~ttagrevatt/vlav/works_pans.html

From what I could gather, washout-down (better?) flushes contents out the bottom of the pan with greater force and up and over the u-bend, the wash-out (more likely to get blocked??) has a shallower pan and the force of the wash has to push the contents up of the edge of the shallow pan before it goes down through the u-bend, The other is rimless. I guess this is an aesthetic difference that requires better control/direction of the flush water to not splash over the edge as it doesn't have an upside down U channel around the upper edge to control the path of the water. Reuter.de has an English language option on the website and similar pricing.

If you've not looked at Airflow, I'm going with a small commercial unit, the DV1100, which is PH Certified, F7 filters etc. My internal volume is around 1650 m3, so I was otherwise looking at 2 residential units. Airflow will do you a free system design, Bill Of Materials, and target price for you to then take round to their distributors to get the best price.

I'm hoping to use sun position to define slat angle, and temp to decide if they are needed at all.

Where does the light "leak" through? I knew those with wire guide can let the light through the holes for the wires, but I was hoping the tracked version, with edges tucked behind the cladding, would give pretty good coverage. I'm assuming yours is connected up to your Loxone. That's the way I'm going.

I'm going with Hunter Douglas external venetian blinds that will be tucked behind the timber cladding. For a 2.1m drop you need about 220mm above the window to retract them and they need a head box 120mm deep (for an 80mm slat), they have guides on the sides, either an extruded channel or wire. When we first quoted HD installed as well as supplied, but when I've gone back to order they no longer install so I've been passed to one of their "partners" to requote.

I have the same concern. Dritherm is vapour permeable, but the K12 is not, so your OSB is in trouble. Even with a vapour check layer on the inside (foil backed plasterboard???) I would have thought you should still have reducing vapour resistance to the outside if you have a vapour permeable main insulation.

That seems really efficient to me, and much quicker than I would have expected. How granular have you gone with your fabric model? Do you have approximate U Values for walls and roof or have you modelled all potential cold bridge areas ie. extra structure around windows, doors, eaves and true timber fraction etc. I'm sure it's a case of diminishing returns (to accuracy), and no idea at what point the critical mass of detail is achieved. In my case I wasn't willing to reduce glazing to a sufficient level so have used automated external blinds to bring the overheating risk into the excellent range. In PH Certification context, I don't believe that means it has been designed out, whereas if I had used fixed brise soleil it would have done.

+1 It was explained to me the % overheating is in respect to the number of hours per year that would be over 25 degrees. PH rate the scale as: 0-2 Excellent, 2-5 Good, 5-10 acceptable However, working through this with Rod Williams, we didn't feel 5-10% was at all acceptable, so we made changes to bring the initial risk of 15% down to 1.5%. However, the advice I got was to not rely on manual processes like having to physically open a vent. Ideally you'd get to the Excellent range by passive means, and if not possible* then by automated means. * = not willing to compromise on that large glazed facade Once you are in the Excellent range there should then be manual process (opening windows etc.) available to then resolve the "extreme" conditions.

Out of interest, those that have done the PHPP themselves, how many hours do you think you spent using the PHPP software to initially model and then iterate the design options? I liked the thought of doing it myself, but felt it would end up demanding more hours than I had available at the time.

If you "hung out" on the AECB Forum and posted a few questions then in the passed you may have got a few contacts, but I'm not sure how busy that Forum is these days. Other than that, you've probably asked in the right place and some recommendations will likely come along. I used Dr. Roderick Williams of Williams Energy and thought he was very good. I used him due to his association with Touchwood Homes, who supplied my frame. I'm pretty sure he takes on non-Touchwood work.

Are you estimating the solar gain based on a hunch, or are you thermally modelling the building (PHPP)? If you plan insulate and airtight close to PH levels you may not need much glazing to get all the solar gain you require. If you design in too much glazing you may give yourselves an overheating issue in summer and possible the shoulder months. If you want the double-height glazing for aesthetic/lifestyle choice then that's absolutely fine, but get it modeled so that you know if an overheating risk requires mitigation.

"Real World" performance is nowhere near that declared to the Regulator! If it ever happened in Automotive there would be a scandal.

Apart from being pretty good at frame design, engineering and erection, one of their guys regularly flies his drone around taking pictures, so you get a great record of the build:

You may wish to reconsider this statement.

On my window install the gaps were sealed externally with silicon bead because the expanding foam is not water tight.

An article on a PH house overheating does not equal PHPP being unable to accurately predict solar gain. On the study I found and read regarding the block of housing association flats that were the subject of Telegraph story a while ago, it was not the tools at fault, but lack of experience from the PH Designers. There will be localised issues with any design/build process, mistakes happen. PHPP however gives you the tools to predict and test solutions so that risks are reduced. It's to be applauded, not condemned. Solar gain issues are present in many standard building regs builds. My current property, with it's room in roof, will regularly see 30 degrees in summer, when it's only mid-twenties outside. But nobody will have done any thermal modelling, so there's no one to blame.

PassivHaus Institut claims there to be 60,000 Certified buildings in use in 2016. Checking the EU market, there were 880,000 Residential HRV units installed in 2015. Around 25% were localised/room only HRVs, with 75% being centralised systems. Germany, Austria, Switzerland being the more mature markets, UK expanding fast (double-digit growth), but lagging behind. Understandably HRV's are concentrated in Northern EU. [Non-heat recover ventilation units being nearly double the volume, but concentrated more to Southern EU.] Hardly a small market. There's a few sizable studies into MVHR/low energy homes/zero carbon homes that do detail MVHR issues with poorly maintained systems and lack of knowledge of occupants, but none suggest systemic/technology issues. However the one study that reports it, shows that even in houses with sub-optimal MVHR performance the air quality is better than the naturally ventilated houses in 80% of the those tested. This is not a new technology, it is not even a niche technology. If there were inherent flaws in the technology the data would be there to demonstrate it. If it's available I'd like to see it so that I am better informed. Without doubt there will be "local" issues with individual builds, there are too many variables for there not to be. PH principles put occupant comfort at the centre of its strategy, along with energy efficiency and affordability. The PHPP software aids making the decisions and compromises that come into balancing those three competing requirements. Most telling though is that it also informs the heating requirements for a building. If it didn't accurately analyse the environment and predict the energy usage then those people relying on it to size the heating systems would find themselves with properties they were unable to heat sufficiently. If that were the case there would be quite a few of those 60,000 customers very understandably making their voices heard... But I don't hear them... I must assume the PHPP software to be relatively accurate. But why wouldn't it be, it's "only" physics after all.

Or, could you have 3D cold bridging in the corners causing a significant cold point that is below dew point for more of the time?

That's quite an old study that was discussed over at eBuild, JH referred to it quite a few times. I don't agree with the title. Came down to poor installation of the underground duct.

Like I said, I'd searched, but found any data to support your assertion elusive, so thought I'd give you the opportunity to post a reference. But if it doesn't exist, it can remain an 'intersting' theory.? And my comments on eddy currents are informed by my knowledge of automotive aerodynamics and CFD analysis. Your statement may be correct in the context of vehicle aero, but that's not the context of this discussion.

Anything Google can find for you will be OK with me. I've found several large scale studies into MVHR systems in domestic homes, and most are critical about sub-optimal performance of poorly maintained systems or occupants unfamiliar with the correct use, but none comment on the phenomenon you mention, which is odd as it would be quite a serious failure. No, not really. Eddy currents for one will be caused around any sold objects, nothing like light. I'm certainly not convinced about the potential of mold growing within the thermal envelope of a PH-level insulated home. RH would need to be too high for too long, due to the temperature of the internal faces of exterior walls and even windows. Within the cavity, or outside the thermal envelope, if there is poor detailing, is another subject.

Could you post a reference please. In an occupied house with people moving around, doors being opened and closed, convection currents and the MVHR extract and return vents I would naturally have considered the internal air volume to be well mixed, but you seem to be suggesting that with even with a theoretically sufficient ventilation rate from the MVHR unit, you could still get poor circulation to such an extent that localised areas of high RH could cause mold growth. I'd like to understand better the mechanics of how that could occur. Edited to add: Just did a little calculation, it would need the RH to sit at +80% for a week to promote mold growth in a typical PH insulated home, if there were no cold bridging issues causing a cold spot that brought the temperature of the internal face of the wall below what you would otherwise expect.

I'm putting 100mm into 95mm studs following the advice from Rockwool that it will easily compress down. I assume though that performance will drop of if it's compressed too much. I got good prices locally from Collier & Catchpole BM But the cheaper RWA45 Acoustic insulation is not available in as many sizes as the FlexiSlab. I've therefore gone with a mixture of RWA45 and FlexiSlab The problem for me was RWA45 doesn't come in 400mm wide and cutting down 600mm was higher cost than buying 400mm FlexiSlab.