Raising a house's EER to 7 or 8 « Alternative Technology Assn Forums

Alternative Technology Assn Forums » Sustainable Building

Raising a house's EER to 7 or 8

(37 posts) (10 voices)

Started 1 year ago by gav3500
Latest reply from dave lawrence

Tags:

« Previous 12

Greg C
Member

I have lived in a passive solar house in Sydney for 20 years. My observations based on that are as follows

Shading: Mine I work to a 65 degree angle. That means full shade from late October to late February. That is a compromise and basically you could do with more sun on the October side and less on the Feb side. Autumn is usually warm and sees the house overheat in March and April, easily dealt with via cross ventilation.

Pergola: My pergola does the shading. It has fixed blades of 13mm plywood set at 32 degrees and overlapped so that full blockage occurs when the sun is higher than 65 degrees. In winter, the sun penetrates about 3.5 metres into the house Forget about effective height of the windows. What you are interested in is when the sun sneaks in through the bottom and when it does not.

Thermal Mass. We have a concrete slab floor with black slate. It works very well. If management wants timber floors you will need to get some heated mass some other way. I have always liked the Trombe-Michel idea, and it can be adapted to other situations as well. I would suggest you glaze the entire north face (double glazed) and if you want some solid wall in one area use the Trombe-Michel idea. Could be masonry, water in drums or bottles etc.

The old house should be double glazed throughout, and for better solar heating there are a few add on systems that can pump warm air into the old house. eg http://www.hrv.com.au/

Our house can't really get through a Sydney winter without some boost for one month from a fan heater. Double glazing was too expensive 20 years ago and I think it would tip the balance if we could retrofit. 18 degrees is the lowest temp the family will accept which works very well in that boosting is needed infrequently. The lowest temp the house has got to is 14.9c, in the morning and from that temp it would need 2 or more sunny days to build up any reserve. Canberra is much colder than Sydney so insulation is very important. Have you considered reverse brick veneer, with that you can get very good wall insulation and the mass is where it is needed.

regards

Greg

Posted Saturday 9 Oct 2010 @ 10:49:42 am from IP #
gav3500
Member

Hi Greg,
Thanks for that. Somewhere around 65deg for summer seems reasonable. Canberra is a little hotter than Sydney but the change is more abrupt. Could your use of louvers also contribute to your winter heating problems. Louvers block a portion of sun even when it is at the right angle and then more as the azimuth changes. It is probably simple math to work out the total loss from louvers or at least graph how it changes over the day.

I have considered reverse brick veneer. My wife is not fond of the appearance and durability. Also with one wall on the old house and one facing north that leaves two left. One of these is mostly kitchen and cupboards. Best outcome will be double brick in the south west corner and brick veneer everywhere else. There are few internal walls in the new house for use as masonry.

Currently working on R6 in the ceiling (AusZeH has R6) and whatever fits in the walls. I've allowed 250mm for brick veneer walls. So they will likely contain fibreglass plus reflective building wrap. The double brick sections will have EPS. Slab will have waffle pod for insulation and I'm working on what edge insulation is possible.

What do people do for wiring in double brick houses? I'm guessing some form of decorative finishing 600mm off the floor through which wiring can be run.

The north facing design is here
https://sites.google.com/site/gavspace/house-extension/north-extension

Posted Monday 11 Oct 2010 @ 4:24:24 am from IP #
dymonite69
Member

The Your Home Technical Manual Shading formula isn't recursive. If you perform a simultaneous equation calculation you can work out that the under eave distance is 0.43 x window height.

As can be seen, the taller the window, the bigger the gap. Tall windows are difficult to fully shade.

The other point is that technically you have to either vary gap height or eave length for different window heights. Usually you settle on an average.

It is better to avoid tall windows if you want better control over summer shading.

Posted Monday 11 Oct 2010 @ 5:36:34 am from IP #
dave lawrence
Member

re : double brick house wiring it goes in cavity.
re comments on your house extension , if you go with clerestorey roof as shown over existing bedroom why not run clerestorey roof section all the way to existing roof ridge ,otherwise you create undesirable flashed section on top of roof where existing roof plane runs down toward new high wall. (leaving future potential leaks and unwanted out of sight out of mind maintenance hassles )
I see why you are doing "cut' (AKA pitched ) roof, with roof that custom will be very time consuming and costly. I would advise squaring it off ,you can still leave the extension on that angle to the house ,just square it off where you can .
Then you could at least truss part of the roof.

Posted Tuesday 12 Oct 2010 @ 1:35:26 am from IP #
dave lawrence
Member

to gav3500 had a re- read of your post regarding wall thickness. you can in fact get extra wide cavity ties BUT most builders and brickies are NOT USED to doing anything outside the square ( and will do their utmost to avoid doing so !!! ) SO I Suggest if you are contemplating extra wide cavity (A VERY GOOD IDEA ) then you will need to do the research and source the cavity ties for the builder and ENSURE that he is AWARE OF YOUR NEEDS IN THIS REGARD before signing contracts . I SAY THIS from experience and wish it was different but to date I have been frustrated on most jobs by builders VERBALLY agreeing with client requests only to change what they see as minor details themselves later. AND nearly always due to lack of forward planning and ordering materials.
GOOD LUCK !!

Posted Tuesday 12 Oct 2010 @ 2:01:32 am from IP #
gav3500
Member

Thanks for your comments Dave. Yes extending the celestory section to the ridge seems reasonable. That's actually a new bedroom under it and would replace the existing dining/kitchen. By "cut" roof I assume you mean the three part hip section on the western end. It reflects the taper in the floorplan which is there because I was running into the fenceline. Moving it the extension northward to square it off brings it too close to the garage. I could square off the northern facet but the south is problematic. If I just hang the roof over the tapered southern corner it will overhang about 1.5m. Quite a lot, though still short of the fenceline. An important thing to discuss with the builder/architect.

The 30deg pitch on the roof is for PV (not the ideal pitch but at least 30deg is relatively standard). Solar HWS may need to go on the northern roof of the old house.

I thought this shape might be expensive so I have a cheaper but less efficient shape which I will post soon. The idea was to compensate on the inefficient shape with active measures (hopefully costing less than the difference).

As for wall thickness I was just trying to say standard walls, which are 10" on the existing house. But now that you mention it what are the benefits of an extra wide cavity? I might have another 100mm to play with.

In a standard brick veneer setup you could flesh it out as brick, cavity, 20mm batten, foil wrap, 90mm wood frame with 83mm fibreglass batt (R1.5), foil wrap, 20mm batten, gyprock. The foil combining with fibreglass to give > R2 and work with the extreme hot and cold in Canberra.

I was thinking with double brick that in what I've seen the cavity gets filled up with EPS so any future wiring needs to be run on the interior surface of the wall.

Posted Wednesday 13 Oct 2010 @ 3:02:48 am from IP #
dave lawrence
Member

extra wide cavity provides extra space for extra insulation and still allows for drainage aspect of cavity. The drainage aspect of Cavities functionality are often compromised by overzealous builders/owners squashing insulation in , thus bridging the space required for efficient drainage. make sense ?
without further studying the plans I still quite like the idea of squaring off the roof even if it means the 1.5 m overhang in the southern corner as you suggest. BY cut roof , I was actually referring to the entire new section.

Posted Wednesday 13 Oct 2010 @ 7:26:09 pm from IP #

RSS feed for this topic

« Previous 12

Reply

You must log in to post.