The importance of good design

waqasahmed

I've seen the typical memes over the past few days given our summers are getting too hot now where people talk about how our houses are built primarily to retain heat and Americans getting confused as to why we don't have AC even if only used temporarily 

I was reminded of what a PassivHaus architect said. With good design and good ventilation, you drastically reduce your requirement for AC.

I figure this makes sense on two grounds 
- The first is that humans have been cooling themselves in buildings for thousands of years before the discovery of electricity.  Prehistory might have been in caves, but civilisation itself is only about 12000 years old and you don't see articles about people dying en masse due to heat stroke in ancient Mesopotamia, especially in the cities where the heat builds up

- The second is that in my parent's country (Azad Kashmir, Pakistan), the temperature can get up to 40C and like here, in the UK it gets extremely humid.  Climate change has exacerbated heat issue in both countries ofc too

I found that when I visited there, the house was so much cooler than our house in the UK despite the fact that we have no AC. Most British Pakistanis do have AC tbf but we don't . We've just got fans which also stop working when it gets too humid. 

Good design and good ventilation means that the house is reasonably fine in temperature even when there are power cuts which is quite frequent. It's  not as bad as the UK when the fans slow down. 

In that sense, I think I've seen first hand exactly how good design means that as the country gets hotter, things like an MVHR and improved insulation should also drastically reduce the requirement for AC in the UK where AC units are expected to explode in popularity, which has a negative feedback loop ie: the more AC units installed, the quicker we warm up the planet, so we need ever more ACs

The longer I can put off AC (and others), the better. I just wish the government would be able to help out with retrofitting MVHRs where possible, and insulating the tops of flat roofs which aren't currently covered by eco4 grants. I'm not currently eligible for any such grant but it would sure help those who most need that help, and who knows. I might need that help some day too

JSHarris

We live in a passive house.  I designed it in 2012 and did a lot of the building work myself over a 4 year period.

The heating requirement is very low (we average around 12kWh/m²/year, so slightly under the PassivHaus limit).  There is very much a cooling requirement though, as the house settles at the mean daily temperature in summer, plus the temperature rise from occupants, cooking, appliances, etc.  The latter alone is enough to heat the house to a comfortable temperature for October to mid-December, and through March and April. 

However, in summer that heat from just living here needs to be got rid of.  Ventilation helps, we have MVHR and use that to night purge when the outside air is cooler.  Doesn't do away with the need for cooling though, as air has such a low heat capacity that even shifting tens of m³ of it overnight doesn't give a lot of cooling

The active cooling requirement is very modest though.  We have a single 2.5kW A2A unit upstairs that is way too powerful on full, even on the hottest days.  We run it mostly when there's enough solar generation to make running it free, which isn't hard as it rarely averages more than around 300W electrical input power.

For those unfamiliar with the PassivHaus standard, it's an energy performance that is several times better than required by British Building Regulations.  So much so that it makes the Energy Performance Certificate a complete joke.  Our 2016 EPC is supposed to have a maximum for band A of 100.  Our house scored a nonsensical  A107, which caused our local building control people to question our assessment.

waqasahmed

JSHarris said:

We live in a passive house.  I designed it in 2012 and did a lot of the building work myself over a 4 year period.

The heating requirement is very low (we average around 12kWh/m²/year, so slightly under the PassivHaus limit).  There is very much a cooling requirement though, as the house settles at the mean daily temperature in summer, plus the temperature rise from occupants, cooking, appliances, etc.  The latter alone is enough to heat the house to a comfortable temperature for October to mid-December, and through March and April. 

However, in summer that heat from just living here needs to be got rid of.  Ventilation helps, we have MVHR and use that to night purge when the outside air is cooler.  Doesn't do away with the need for cooling though, as air has such a low heat capacity that even shifting tens of m³ of it overnight doesn't give a lot of cooling

The active cooling requirement is very modest though.  We have a single 2.5kW A2A unit upstairs that is way too powerful on full, even on the hottest days.  We run it mostly when there's enough solar generation to make running it free, which isn't hard as it rarely averages more than around 300W electrical input power.

For those unfamiliar with the PassivHaus standard, it's an energy performance that is several times better than required by British Building Regulations.  So much so that it makes the Energy Performance Certificate a complete joke.  Our 2016 EPC is supposed to have a maximum for band A of 100.  Our house scored a nonsensical  A107, which caused our local building control people to question our assessment.

Oh for sure. It doesn't entirely get rid of cooling requirements but it does seriously reduce your requirements for cooling 

I'm not looking to completely go PassivHaus on a retrofit but I will for an extension. For a retrofit it is a lot more effort to go PassivHaus for little gain unfortunately 

Brie

MVHR?  translation please!!!

JSHarris

Brie said:

MVHR?  translation please!!!

Mechanical Ventilation with Heat Recovery.  The unit draws air from extract ducts installed in bathrooms, the kitchen, WC and utility room, then passes it through a heat exchanger before exhausting the air to the outside.  Incoming fresh air passes through a pollen filter and then through the other side of the heat exchanger, before being fed to ducts in every habitable room.

The result is a high ventilation level all year around, with about 85% of the heat that would be wasted from normal ventilation being recovered and passed to the incoming outside air.  This means no cold draughts, despite the high ventilation rate.  To work effectively the house has to be pretty airtight, a lot more airtight than required by building regulations.  The whole inside of our house has a taped up airtightness barrier, the door and window frames are taped and sealed to this.  The doors and windows are all PassivHaus certified, so have triple seals for airtightness as well as 52mm thick triple glazing.

The result is a house with very little dust and very fresh-feeling air, as well as low heat losses.  Our house would lose around three or four times more heat if we didn't have the MVHR system.

Brie

so being taped up there's no open windows or doors.  I'm not sure I could cope with that.  I'd have to find a place that was all done and see if it was ok before paying to have work done.

JSHarris

Brie said:

so being taped up there's no open windows or doors.  I'm not sure I could cope with that.  I'd have to find a place that was all done and see if it was ok before paying to have work done.

The doors and windows open as normal, although we very rarely ever bother to open any windows, as there's no need to.  The airtightness tape just seals the outer frames to the airtight barrier material that lines the whole inside of the house (behind the plaster).

Only other thing to note is that we couldn't have a conventional letter box - that would leak so much air as to undo all the work done to make the house airtight.  Instead we have two boxes outside, a letter box at the front and a secure parcel box (a Brizebox) by the back door (just so it's less visible).   I did also have problems with air leaking through the keyholes at first.  During the air leakage testing they howled like banshees.  Easily fixed by injecting very thick silicone grease deep into the locks.  Doesn't affect the keys, as the doors are about 120mm thick, so the keys don't get close to the plug of thick grease in the middle.

waqasahmed

JSHarris said:

Brie said:

so being taped up there's no open windows or doors.  I'm not sure I could cope with that.  I'd have to find a place that was all done and see if it was ok before paying to have work done.

The doors and windows open as normal, although we very rarely ever bother to open any windows, as there's no need to.  The airtightness tape just seals the outer frames to the airtight barrier material that lines the whole inside of the house (behind the plaster).

Only other thing to note is that we couldn't have a conventional letter box - that would leak so much air as to undo all the work done to make the house airtight.  Instead we have two boxes outside, a letter box at the front and a secure parcel box (a Brizebox) by the back door (just so it's less visible).   I did also have problems with air leaking through the keyholes at first.  During the air leakage testing they howled like banshees.  Easily fixed by injecting very thick silicone grease deep into the locks.  Doesn't affect the keys, as the doors are about 120mm thick, so the keys don't get close to the plug of thick grease in the middle.

For me, I've got like a cloak room before you enter the wider house, so I can still have my letterbox and have a PassivHaus door after the cloak room instead 

I did look into replacing the "cloak room" door (which is that the first door into the property), and get an external letterbox instead like yourself but given I've got a cloak room, it seems like it's an unnecessary cost.

If anything, the second door can be completely air tight for me with no key hole at all so this is again, the cheaper option.

I've also read that an MVHR improves heat recovery across ALL levels of air tightness too despite what was initially thought but the best results are when it's super air tight 

JSHarris

waqasahmed said:

JSHarris said:

Brie said:

so being taped up there's no open windows or doors.  I'm not sure I could cope with that.  I'd have to find a place that was all done and see if it was ok before paying to have work done.

The doors and windows open as normal, although we very rarely ever bother to open any windows, as there's no need to.  The airtightness tape just seals the outer frames to the airtight barrier material that lines the whole inside of the house (behind the plaster).

Only other thing to note is that we couldn't have a conventional letter box - that would leak so much air as to undo all the work done to make the house airtight.  Instead we have two boxes outside, a letter box at the front and a secure parcel box (a Brizebox) by the back door (just so it's less visible).   I did also have problems with air leaking through the keyholes at first.  During the air leakage testing they howled like banshees.  Easily fixed by injecting very thick silicone grease deep into the locks.  Doesn't affect the keys, as the doors are about 120mm thick, so the keys don't get close to the plug of thick grease in the middle.

For me, I've got like a cloak room before you enter the wider house, so I can still have my letterbox and have a PassivHaus door after the cloak room instead 

I did look into replacing the "cloak room" door (which is that the first door into the property), and get an external letterbox instead like yourself but given I've got a cloak room, it seems like it's an unnecessary cost.

If anything, the second door can be completely air tight for me with no key hole at all so this is again, the cheaper option.

I've also read that an MVHR improves heat recovery across ALL levels of air tightness too despite what was initially thought but the best results are when it's super air tight 

There is a law of diminishing returns when it comes to airtightness versus MVHR efficiency for sure.  Depends a lot on where you live, particularly the exposure to wind.  Where we are (bottom of a deep valley, house cut back into a south-facing hillside) we could have got away with a lower level of airtightness (our air test was 0.49 ACH @ 50Pa).  We never experience high wind speeds here, certainly no where near high enough to see a 50Pa pressure differential between inside the house and outside.  Might be different if we lived on the top of a hill, or an exposed coastal location though.

Having an external letter box, and particularly the external parcel box, is something we now think is a benefit.  Both are pretty secure, and more importantly don't give away any clues as to when we are away.  Both our front door and back door are glazed, so removing a clue to potential burglars that we may not be in provides a degree of reassurance.  It's no great hardship to get the keys and go and check either box.

waqasahmed

JSHarris said:

waqasahmed said:

JSHarris said:

Brie said:

so being taped up there's no open windows or doors.  I'm not sure I could cope with that.  I'd have to find a place that was all done and see if it was ok before paying to have work done.

The doors and windows open as normal, although we very rarely ever bother to open any windows, as there's no need to.  The airtightness tape just seals the outer frames to the airtight barrier material that lines the whole inside of the house (behind the plaster).

Only other thing to note is that we couldn't have a conventional letter box - that would leak so much air as to undo all the work done to make the house airtight.  Instead we have two boxes outside, a letter box at the front and a secure parcel box (a Brizebox) by the back door (just so it's less visible).   I did also have problems with air leaking through the keyholes at first.  During the air leakage testing they howled like banshees.  Easily fixed by injecting very thick silicone grease deep into the locks.  Doesn't affect the keys, as the doors are about 120mm thick, so the keys don't get close to the plug of thick grease in the middle.

For me, I've got like a cloak room before you enter the wider house, so I can still have my letterbox and have a PassivHaus door after the cloak room instead 

I did look into replacing the "cloak room" door (which is that the first door into the property), and get an external letterbox instead like yourself but given I've got a cloak room, it seems like it's an unnecessary cost.

If anything, the second door can be completely air tight for me with no key hole at all so this is again, the cheaper option.

I've also read that an MVHR improves heat recovery across ALL levels of air tightness too despite what was initially thought but the best results are when it's super air tight 

There is a law of diminishing returns when it comes to airtightness versus MVHR efficiency for sure.  Depends a lot on where you live, particularly the exposure to wind.  Where we are (bottom of a deep valley, house cut back into a south-facing hillside) we could have got away with a lower level of airtightness (our air test was 0.49 ACH @ 50Pa).  We never experience high wind speeds here, certainly no where near high enough to see a 50Pa pressure differential between inside the house and outside.  Might be different if we lived on the top of a hill, or an exposed coastal location though.

Having an external letter box, and particularly the external parcel box, is something we now think is a benefit.  Both are pretty secure, and more importantly don't give away any clues as to when we are away.  Both our front door and back door are glazed, so removing a clue to potential burglars that we may not be in provides a degree of reassurance.  It's no great hardship to get the keys and go and check either box.

I do live on top of a hill, but honestly, I could get away with not leaving my door locked. I do it out of habit mind but still 

Regardless, I'll still be opting for the best possible form of air tightness and really, the majority of that is your big gaping holes in your property (ie: windows and doors)

If you can sort out the big gaping holes, then you've pretty much automagically sorted out how airtight your house is. 

JSHarris

I tried to improve the performance of our old house, with only limited success.  The insulation was fairly easy to improve, as were the doors and windows (they needed replacing anyway).  Airtightness was a very difficult thing to improve I found.  I made up a Heath Robinson contraption, using an old car radiator fan, fitted to a bit of board.  I taped this into a window and wired the fan up to a 12V power supply and variable speed controller.  This allowed me to suck air out of the house and go around looking for air infiltration.

The shock to me was just how much air/draughts was coming in from places I didn't expect.  All the double glazed door and window seals leaked to some degree, but the worst airleaks were tiny cracks between the ceiling and walls, plus air leaks around all the light switches and sockets.  Air was leaking from the loft down into the house in dozens of places.  With hindsight I should have realised this, as there always seemed to be spider's webs and woodlice behind outlets and switches.  The only way they could have got there was by crawling in from the loft space.