Build method options

[Red Kite]

Hi, we were planning to build in timber frame - well insulated with good air tightness and MVHR  - typical of what a lot of folks here seem to build and some ways down the PH route. Talked to SE and  he  was very much in favour of high density blockwork  / high thermal mass and passive stack type ventilation. External insulation layer and plaster internal layer for air tightness. This was a total curve ball so I wanted to put the debate out there to see what other more knowledgeable folks thought. Any comments?

[scottishjohn]

 

will this be a turnkey project?

or you self build

research ICF--

just google ICF building systems

If heading close to passiv --then ICF type is easier 

lots of choices from polystyle ICf to woodcrete blocks +panels 

you will attain good air tightness easier with ICF +also gives you the thermal mass .

you can do it with block work -- as well--investigate  before making decisions

my suggestion would be to get  the  design .then you can get prices from different suppliers for cost of main shell +roof 

internals will be  basically same with any house build

there are no wrong ways .but some may suit you better

 

Edited January 31, 2019 by scottishjohn

[Jeremy Harris]

Worth reading this thread, perhaps:

 

There's really no such thing as "thermal mass" at all, it's a made-up term, that describes something that cannot be measured and has no units of measurement associated with it anyway.

 

It's easy to build a timber frame house, without any masonry, that has a long thermal time constant.  We've done just that; our house is all-timber (except for the foundation slab and slates) and has a thermal time constant that is a lot longer than 24 hours, which means that temperature changes between day and night are effectively ironed out.

 

The key thing is to ensure that the structure ends up with a long decrement delay.  There is a useful article on decrement delay here: http://www.greenspec.co.uk/building-design/decrement-delay/ that describes what it is and why it's important.  In general, using low heat capacity construction will tend to give a low decrement delay, whereas a high heat capacity structure with the same overall U values will give a long decrement delay.  We opted to use 300mm of blown cellulose in our walls, and 400mm of it in the roof, which has given us a structure with a long decrement delay, and hence long thermal time constant.

 

[Big Neil]

Nudura have a bunch of good instructional videos on their YouTube channel, as do FoxBlocks although the latter is not available over here. I look at them a fair bit to try and understand the method as a whole. It seems to me having wondered this very topic myself and spent hours on here, that the broad answer is that any system can give PH if detailed correctly. Have a read of @JSHarris and @Russell griffiths blogs for good detail on timber frame and ICF respectively. Obviously there are others, but I look at these two a fair amount.

 

Try and think of Speed, Quality and Low Cost. I've always got them floating around my head. remember you can broadly have any two but not a third.

[Nick1c]

Tony on greenbuildingforum built a well insulated high density block house, he also had a website/blog - Tony's house reading iirc (the 'Tony tray' is worth looking at). 

As others have mentioned a good result can be achieved using any of these methods, which is most appropriate will be specific to your circumstances. Site access and the availability of trades will be key. As far as I can see attention to detail is vital to achieve good air tightness and insulation performance, for this reason I would avoid rigid insulation internally as gap filling would be difficult. Sheathing a building with eps sheets or blown insulation sounds fairly simple to get right. 

[Red Kite]

Wow, much much more complex than I thought possible for such a 'simple' thing as a house! Many thanks for the info on decrement delay etc - my head is spinning! It would seem that the SE possibly doesn't understand it either but at least I am consciously incompetent!

 

I guess that the other part of this is that the real thing about a passive house is that it is ideally just that - passive i.e. no heating and no cooling and it is just immune to external weather conditions. However if in the real world you have a house that does at times need some heating or cooling you need to provide that and control it. At that point you need a heating and cooling system that works best with the thermal time constant of the building in terms of delivery method - for example heating with UFH (long time constant) or say MVHR air heating (short time constant). It seems that the characteristics of a heating and cooling system dont want to be the same since the need for cooling comes from fairly rapid solar gain whereas heating comes from much slower overall weather conditions.

 

So it would seem that as well as considering the time constant / thermal decrement / insulation properties of the house you need also to design heating and cooling that complements that. Or rather makes up for the inadequacies of the building. Also since we are talking low energy etc then the costs of these systems (capital and running costs)  need to be taken into account - which is where PH started from I think  i.e. very comfortable buildings with low running costs!

 

If our goal is overall comfort and very little changes of internal temperature  then the delivery and control of heating and cooling become a consideration so does anyone have any ideas on that - other than design the building so it hardly matters!

[le-cerveau]

SE is looking at a simple structural method (easier for him) to reduce complexity.

The SE is simply there to do the calculations based on your requirements, and advise if not possible and alternatives, not shape your whole build.

Depending on the size and shape of your house, plot conditions, location, local environment, some methods will be more beneficial than others.

 

We went ICF, because a) we wanted a solid economical house but more importantly I had 12m spans that could only be done with precast slabs, which limited the options.  Managed to get the spans down to 8m (max practical) with a single steel and post without affecting the plan.  That was done my my AT (Architectural Technical) not an SE.  My AT employed SE's where required for specific jobs.

[Dreadnaught]

@Red Kite Ben Adam Smith of the House Planning Help podcast went with a masonry constructed certified passive house for his own personal build. Might be worth your while looking that up. His was also a turnkey project with a prime contractor supervised by an architectural firm and thus expensive.

 

I have chosen a different route for my soon-to-be-built bungalow (passive slab, TF, self-managed build without prime contractor).

Edited January 31, 2019 by Dreadnaught

[Gone West]

3 hours ago, Red Kite said:

Hi, we were planning to build in timber frame - well insulated with good air tightness and MVHR  - typical of what a lot of folks here seem to build and some ways down the PH route. Talked to SE and  he  was very much in favour of high density blockwork  / high thermal mass and passive stack type ventilation. External insulation layer and plaster internal layer for air tightness. This was a total curve ball so I wanted to put the debate out there to see what other more knowledgeable folks thought. Any comments?

Too high a 'thermal mass' building can feel uncomfortable if you like a fairly constant warm indoor temperature. If you live in an unshaded, sheltered spot then as has been mentioned decrement delay can be very important. There are different ways of dealing with the problem, the easiest of which is to let the climate deal with it for you. If, as we do, you live in an area where it's always windy, it isn't a problem. Passive stack ventilation can be weather dependent so MVHR is more reliable at delivering the correct amount of ventilation.

[joe90]

5 minutes ago, PeterStarck said:

Too high a 'thermal mass' building can feel uncomfortable if you like a fairly constant warm indoor temperature.

 

I have never heard that before. The whole point of high mass is to keep temperatures steady. We have a “heavy house”, block brick etc just like Tony,s house. Because it is heavy, well insulated and good decrement delay it’s a very steady temperature and heated by UFH with an ASHP. 

[Gone West]

Just now, joe90 said:

 

I have never heard that before. The whole point of high mass is to keep temperatures steady. We have a “heavy house”, block brick etc just like Tony,s house. Because it is heavy, well insulated and good decrement delay it’s a very steady temperature and heated by UFH with an ASHP. 

I guess it should be fine in a perfect house but it's something we experienced at a friends house. They couldn't keep the ground floor at the temperature they wanted because it was very slow to react to heating and cooling. The ground floor was high density concrete block but the first floor was timber frame. We found the temperature variations between the two floors uncomfortable. It certainly wasn't a steady 23C over the whole house.

[Jeremy Harris]

I've never been sure why mass seems to be connected to the thermal time constant of a house, as the factors that control that are mainly heat capacity and thermal conductivity, with ventilation rate playing a small part (assuming the house is fairly airtight).

 

I agree that having a very long thermal time constant can pose a challenge for the heating control system, as you can get to the state where the heating system has to try and predict the amount of heat to inject into the house many hours before, so if the temperature changes in an unpredictable way the heating system can get caught out.  This happened to us this week, as the temperature suddenly dropped a lot and the slab wasn't really warm enough to maintain the temperature.  For the first time in ages I turned the temperature up on the MVHR and warm air at ~40 deg C from the MVHR fresh air supply terminals did warm the house up over the course of a couple of hours.  I can't say either of us really liked this much, though, as the RH dipped down to about 27%, which we find a bit too dry. 

 

Most of the time I find that just charging the slab up overnight at the E7 rate seems to work fine, as to some extent the temperature then becomes self-limiting.  If the house warms up from solar gain, cooking etc, then the slab just reduces or stops heating the house, as the temperature differential drops.  As the house cools, then the heat output from the slab increases to warm it back up, from the change in differential temperature.  This seems to work OK because our slab sits at around 22.5 to 23 deg C pretty much all the time and the house seems to sit at around 22 deg C or so.  Upstairs, where we have no heating, apart from towel rails in the bathrooms, sits at around 19 deg C, which we find comfortable.

[vivienz]

You can have a house that is built to passive standards rather than a Passivhaus.  Personally, I wouldn't want the latter as I want my home to function around me, not my having to compromise my lifestyle to suit the house.

 

We're into the final stages of our timber frame/passive slab build and I've had the underfloor heating ticking over at a modest 18 C for the last three months or so, powered by electricity feeding into a couple of little willis heaters.  Once we're live with the other systems, they will be fuelled by solar PV.  This choice was dictated by having no gas near the site. 

 

Now, that 18C running through the slab has created a lovely, temperate atmosphere in the building, even though the MVHR isn't running yet.  It's a little cooler upstairs but still very tolerable.  I don't yet know how much it has cost me on electricity so far and I'll report back in due course, but given the high level of insulation I doubt it's costing me anywhere near what it costs to heat our current home.  As I sit here typing at my desk, a nasty cold draft is sneaking in from all directions and I feel far more comfortable, temperature-wise, at the new build.

 

In my limited experience of SEs, I would say go with what you want and then ask them how to build that rather than what they would build.

[Ed Davies]

10 minutes ago, JSHarris said:

I've never been sure why mass seems to be connected to the thermal time constant of a house, as the factors that control that are mainly heat capacity and thermal conductivity, with ventilation rate playing a small part (assuming the house is fairly airtight).

 

When people say “thermal mass” just read “heat capacity”. Saves on the blood pressure.

 

My guess would be that the house @PeterStarck is talking about was not, by the standards of this forum, well insulated. Sort of a re-run of the 1970's mass&glass vs light&tight controversy when now we know the truth (?) mass&tight (with maybe a bit of glass).

 

Still, going back to the OP's question, the tight bit is more important than the mass bit; the mass only helps if you have some intermittent form of heating like sunlight or E7 electricity. If the heat source is directly and easily controllable all the time the mass matters a lot less.

[Mr Punter]

I have seen some fantastic houses in ICF, timber frame and brick and block. All are capable of achieving very high levels of comfort. There are pros and cons to each.

[Gone West]

Just now, Ed Davies said:

 

My guess would be that the house @PeterStarck is talking about was not, by the standards of this forum, well insulated. Sort of a re-run of the 1970's mass&glass vs light&tight controversy when now we know the truth (?) mass&tight (with maybe a bit of glass).

 

That's the surprising part. It was designed by a PH designer to PH standards with a ground floor constructed with high density concrete blocks with a 300mm cavity filled with Rockwool.

[Declan52]

This topic has been covered many many times here already.  Do your research and see what suits your targets.  Listen to all the different pros and cons and then make your choice.  You're the one paying the bills and going to live in it so it's up to you.  

You can have an energy efficient house made using all the  different methods mentioned above. 

[Pete]

38 minutes ago, vivienz said:

You can have a house that is built to passive standards rather than a Passivhaus.  Personally, I wouldn't want the latter as I want my home to function around me, not my having to compromise my lifestyle to suit the house.

 

We're into the final stages of our timber frame/passive slab build and I've had the underfloor heating ticking over at a modest 18 C for the last three months or so, powered by electricity feeding into a couple of little willis heaters.  Once we're live with the other systems, they will be fuelled by solar PV.  This choice was dictated by having no gas near the site. 

 

Now, that 18C running through the slab has created a lovely, temperate atmosphere in the building, even though the MVHR isn't running yet.  It's a little cooler upstairs but still very tolerable.  I don't yet know how much it has cost me on electricity so far and I'll report back in due course, but given the high level of insulation I doubt it's costing me anywhere near what it costs to heat our current home.  As I sit here typing at my desk, a nasty cold draft is sneaking in from all directions and I feel far more comfortable, temperature-wise, at the new build.

 

In my limited experience of SEs, I would say go with what you want and then ask them how to build that rather than what they would build.

I for one will be interested to see how much it is costing you to run the Willis heaters.

[vivienz]

It won't be the cheapest option as I'm on a standard variable tariff with SSE - I didn't want to be tied into a contract until I've finished the build.  I shall report back, but bear in mind that an awful lot of power tools will have been charged during the period, too!

[scottishjohn]

5 hours ago, JSHarris said:

I've never been sure why mass seems to be connected to the thermal time constant of a house, as the factors that control that are mainly heat capacity and thermal conductivity, with ventilation rate playing a small part (assuming the house is fairly airtight).

 

I agree that having a very long thermal time constant can pose a challenge for the heating control system, as you can get to the state where the heating system has to try and predict the amount of heat to inject into the house many hours before, so if the temperature changes in an unpredictable way the heating system can get caught out.  This happened to us this week, as the temperature suddenly dropped a lot and the slab wasn't really warm enough to maintain the temperature.  For the first time in ages I turned the temperature up on the MVHR and warm air at ~40 deg C from the MVHR fresh air supply terminals did warm the house up over the course of a couple of hours.  I can't say either of us really liked this much, though, as the RH dipped down to about 27%, which we find a bit too dry. 

 

Most of the time I find that just charging the slab up overnight at the E7 rate seems to work fine, as to some extent the temperature then becomes self-limiting.  If the house warms up from solar gain, cooking etc, then the slab just reduces or stops heating the house, as the temperature differential drops.  As the house cools, then the heat output from the slab increases to warm it back up, from the change in differential temperature.  This seems to work OK because our slab sits at around 22.5 to 23 deg C pretty much all the time and the house seems to sit at around 22 deg C or so.  Upstairs, where we have no heating, apart from towel rails in the bathrooms, sits at around 19 deg C, which we find comfortable.

reading what you say  and agreeing with most of it  

my thoughts are not to have a very thick slab that I heat  for the very reason you say .

maybe 150mm slab ,then insulation then thick screed and ufh pipes 

At this time my house has ufh in the wooden floor and it can change temp with one hour , there is no thermal mass to speak of ,other than the tiled surface 

so this is why it is in my mind to maybe have a relatively thin heated slab --100mm  say 

so it is easy to keep target floor/room  temp  and also bump it up quickly  if needed 

I have been in too many ufh concrete floored houses where it takes so long for temp in house to change , if it suddenly gets warmer outside  

and  you cannot raise ambient temp that quick with very thick floor slab

the climate here can be summer one day and winter the next  add to that the free heat you get to the floor from passiv solar its hard to get it right all the time 

its usual compromise situation again

[ProDave]

You don't need a really thick slab to keep a house warm for a long time.

 

Our UFH is on a suspended timber floor, and the UFH pipes are set in a 25mm thick dry "biscuit mix" screed, so not a lot of "thermal mass" there.  Yet when the heating goes off it takes a very long time for the house to cool down.  That is all down to the long decrement delay of the insulation and the ammount of insulation in the house.

[Jeremy Harris]

10 hours ago, ProDave said:

You don't need a really thick slab to keep a house warm for a long time.

 

Our UFH is on a suspended timber floor, and the UFH pipes are set in a 25mm thick dry "biscuit mix" screed, so not a lot of "thermal mass" there.  Yet when the heating goes off it takes a very long time for the house to cool down.  That is all down to the long decrement delay of the insulation and the ammount of insulation in the house.

 

 

Very true.  Our slab is 100mm thick, with embedded UFH pipes, and seems to work just fine. 

 

Much of the heat capacity in the house will be the plaster/plasterboard layers inside, as gypsum has a higher specific heat than concrete (it holds around 25% to 40% more heat per kg per deg C than concrete).

[joe90]

Because of illness during our build we ended up with a 100mm slab, 270mm insulation then UFH in a 70mm screed and that appears to work well.

[Ian]

13 hours ago, scottishjohn said:

 

so this is why it is in my mind to maybe have a relatively thin heated slab --100mm  say 

so it is easy to keep target floor/room  temp  and also bump it up quickly  if needed 

I have been in too many ufh concrete floored houses where it takes so long for temp in house to change , if it suddenly gets warmer outside  

and  you cannot raise ambient temp that quick with very thick floor slab

the climate here can be summer one day and winter the next  add to that the free heat you get to the floor from passiv solar its hard to get it right all the time 

its usual compromise situation again

We’ve got UFH in a heavily insulated 100mm concrete floor slab and it’s not very quick changing temperature (not a problem for us). It takes approx 1 hour for every 1 degree C increase in room temperature.

 

if you want a more responsive UFH floor build-up you’d be better looking at installing the pipes into the thinnest flow-screed you can get (approx 50mm thick total)

[scottishjohn]

26 minutes ago, Ian said:

We’ve got UFH in a heavily insulated 100mm concrete floor slab and it’s not very quick changing temperature (not a problem for us). It takes approx 1 hour for every 1 degree C increase in room temperature.

 

if you want a more responsive UFH floor build-up you’d be better looking at installing the pipes into the thinnest flow-screed you can get (approx 50mm thick total)

what temp are you charging the floor at ,cos that will make a difference on reaction time .

I wouldn,t go as thin as 50mm ,but also would not have it in 300mm  slab