Withington Co-operative Eco-house - mvhr

MVHR installations

Robert — Wed, 14 Aug 2013 21:12:42 +0000

I try to visit the house towards the end of each working day, to inspect the day's work (and photograph as necessary). Sometimes I stay and do some work there too - the builders jokingly refer to it as the night-shift. One thing I've been doing is fitting the bathroom MVHR units. The first floor bathroom one now has all the ducts in place (though not yet sealed):

And the ground floor one is almost done - but I need the builders to core-drill the holes for the two ducts to the outside before I can put those in:

The top floor one, which will be by far the most awkward, hasn't been started yet.

Also from today:

75mm PIR now largely fitted, still more taping and snagging to do
some more quotes have come in - we are running over-budget, but managing to claw some of the overrun back elsewhere
E.On rep returned my call, said they discontinued supplying Whispergen and it's effectively unavailable in the UK at present
My contact at Baxi returned my call, asked me to send through details of what we're proposing and he's going to get it checked out for us

Design approach: ventilation

Robert — Tue, 16 Jul 2013 21:44:16 +0000

The topic of ventilation and air flows in dwellings has not, unlike with commercial premises, been given much consideration until recently. House-building methods have traditionally led to what has become known as "ventilation by accident": in other words, there is enough air-flow through the building as a result of unintended leakiness of the fabric, that specific consideration of ventilation has not been needed. This has only significantly changed in the two most recent editions of the building regulations.

Aside from the issue of getting the thermal envelope actually constructed as designed, the difficulty is that good thermal performance requires a high degree of air-tightness, whilst occupants of the building require a supply of fresh air to breathe. One approach (as exemplified by the Passsivhaus design method) is to use a whole-building MVHR system. The advantage of this is that you can make the building as air-tight as you like, because the occupants receive a supply of fresh air in every room via the MVHR system ducts (this is referred to in Approved Document F of the 2010 Building Regs as "system 4").

The downside of whole-building MVHR is that routing of the ductwork creates other design implications, and the systems are rather expensive. MVHR systems are better suited to smaller two-storey buildings (where a significant part of the ductwork can be contained within the loft) than to a three/four storey tall house with habited space within the attic. Given the cost and complexity of such a system, consideration needs to be made of whether it would generate sufficient performance improvement to justify its installation. We received advice from others who have worked on eco-house refurbishments that we were unlikely to achieve, in practice, sufficient air-tightness on our project to warrant installing a whole-house MVHR system.

So this brings us back to natural ventilation. This is permitted in the 2010 edition of the Building Regulations, on the following basis: background ventilation to be provided by trickle ventilators to be fitted to all habitable rooms (in practice these are usually fitted to the heads of window frames); 1cm gap between doors and finished floor covering; and mechnical extract ventilation to be provided to kitchen and bathroom - ie high-moisture areas. The gaps under doors allow through-flow of air between (for example) front and rear elevations, and this, combined with negative pressure from the forced extract when kitchen and bathrooms are in use, is deemed sufficient to provide a supply of fresh air for occupants. This is referred to in Approved Document F of the 2010 Building Regs as "system 1".

We didn't want to go down the whole-building MVHR route but neither did we like the idea of "throwing away" warm air via kitchen and bathroom extractors; so a hybrid approach has been adopted. We are implementing all the elements of system 1, but substituting discrete single-room MVHR units in the bathrooms. These units (the model chosen is Manrose HR100RS) are inexpensive, and the ducting can be easily contained within the suspended ceilings we're fitting to the bathrooms. However, unlike traditional MEV (mechanical extract ventilation) units, MVHR systems are balanced - in other words, they provide just as much air into the room as they take out. This means that they aren't creating the negative pressure that a MEV would, and so a single-room MVHR wouldn't be a contributor to the through-flow of air from trickle vents in other rooms and under doors etc. To compensate for this, we will be ducting the room-side outlet from the MVHR to both the bathroom and to an adjoining room. This means that three out of the six bedrooms will have a supply of fresh air additional to the window trickle vents (the other three will not, but then with the system 1 approach, fresh air would likely be drawn into the bathroom to replace extracted air from the nearest room anyway).

Pipe and cable routes

Robert — Mon, 08 Jul 2013 21:45:20 +0000

In rooms which don't have the original decorative ceiling cornices, we are installing suspended ceilings (plasterboard and timber studwork) below the original ceilings. This creates a free route for pipe and cable runs, which both speeds installation and reduces the amount of notching/drilling of load-bearing elements. Today the joiner has started putting up the studwork - and seems remarkably efficient at doing so.

Bathroom areas will be ventilated using single-room MVHR units (see this article for a more detailed explanation), mounted within the suspended ceiling voids. So I have provided the joiner with drawings showing where access hatches are to be located, for servicing the MVHR units. Having finalised the positions of these, I've also ordered all the ductwork.

The builders have moved off the roof and are now doing the wall-ties. We had a talk about the electrical stuff; I'll be going through everything with the electrician on Wednesday.

Starting work on the roof

Robert — Thu, 20 Jun 2013 21:47:03 +0000

The builders have started work on the roof today. Straight away we've found out that we aren't going to be able to salvage as many slates as expected. Apart from that, it's so far, so good.

I finalised the Velux window specification, including adapting the internal studwork slightly to accommodate the 1m2 smoke vent window. I took the rainwater header tank to the house and went through the design of the tank cupboard etc with the builders, in the space.

The MVHR units arrived - physically, smaller than I was expecting (even though I knew the dimensions!). I'm still to figure out and then order the ductwork. I've pretty much settled on siting the top floor bathroom unit in the to-be-formed plant cupboard.

Meeting electrician and fire alarm guy on-site next Saturday (6 July).

Spoke to the letting agent for the house next door, having had no contact from the owner after the initial phonecall; he was similarly disinterested, and suggested I email the landlord once more (which I duly did).

I was considering a very impressive 1.5 litre vacuum flush toilet called Propelair, which I'd seen at Ecobuild. The downside, apart from cost, is that they only currently do a concealed cistern version - but if we are going ahead with the smaller top floor bathroom, a concealed cistern could be used. However, when I spoke to Propelair, they didn't seem to have a distribution channel set up, and the guy on the phone was quite short with me when I pointed out that neither accepting credit card payments nor offering credit yourselves was not conducive to getting business! Seemed like a startup company (apparently the toilet was only launched at this year's Ecobuild), and although I really like their idea, I was reminded of the risk of buying immature technology, and of buying from a startup company, who could easily go bust/discontinue the product/etc (I was told last weekend at Old Hall that they had to decommission their solar hot water collector because the company had gone bust and they couldn't get necessary parts).

A day of dealing with various things

Robert — Wed, 19 Jun 2013 20:53:00 +0000

Set up a basic site office in one of the bedrooms - desk, chair, whiteboard, drawings on wall.

Had another meeting with the sprinkler company - pipe runs etc pretty much all worked out, and agreement for first fix to start a week on Monday (1 July).

It's awkward to get sprinkler coverage in rooms with sloping ceilings (as we have on our top floor), and as sprinkler coverage isn't required in rooms less than 5m2, I came up with the idea of making the top floor bathroom slightly smaller, to get it under this size threshold (it seems pointless to have sprinkler coverage in a bathroom, but at the end of the day we need to say we have complied with BS9521). This would necessitate omitting the bath from the design, which I didn't see too much of a problem with - and that top floor bathroom was crowded anyway.

The rainwater harvesting system arrived (everything but the underground tank, which is being held back until we get rear garden vehicle access). I specifically wanted the header tank on-site to ensure that the joiner builds the cupboard that will be housing it to the right size. And it was a good job I did, because I found out that, including its lid, it is just a little bit too high to fit in the space between the top of the doorways and the underside of the existing ceiling - so the ceiling will have to be raised in this area. I also hadn't realised that it has a 40mm overflow.

On similar lines, I ordered two of the single-room MVHR units (Manrose HR100RS), which should be delivered tomorrow.

I called Velux technical support to try to understand their somehow rather incomprehensible code numbers; good job that I did, as the guy helpfully pointed out that a smoke vent window is required to have at least 1m2 of opening area, and none of the Velux range with a width that would fit within the existing top floor stairwell would match. His suggestion was to have two smaller windows in-line; the other option would be to adjust the stairwell enclosure (which fortunately is all timber studwork). Need to investigate this and come to a decision ASAP.

This evening I had the future occupants of the house come round and discussed various things with them - all went well, apart from the omitting the bath idea, which they didn't like. We discussed various options including having a bath in the ensuite bathroom, and having an over-bath shower in one of the bathrooms (which I really don't like, as in my experience they always leak sooner or later - structural timbers soaking up water in an eco-house would of course not be good at all!).

Obviously it's not good to be firming up and making adjustments to the design at this stage - hindsight is a wonderful thing!

Withington Co-operative Eco-house - mvhr

MVHR installations

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Design approach: ventilation

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Pipe and cable routes

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Starting work on the roof

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A day of dealing with various things

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