Just started a self-build in Dorset. Exciting times!

[MikeSharp01]

3 hours ago, Gone West said:

When I was modelling my last house, I ran my house design through the PHPP with a range of air infiltration values to see what the effect would be.

Here is ours same basis - seems ok to me - its not a Passive house above 0.6 anyway.

Pressurisation Test Result (ACH)    Specific Space Heating Demand (kWh/m2a) Monthly Method - [Annual Method]
               0.2                                              10.3 [10.9]
               0.4                                              10.5 [11.1]
               0.6                                              10.7 [11.3]
               0.8                                              10.9 [11.6]
               1.0                                               11.1 [11.8]
               2.0                                              12.2 [13.0]

[Russell griffiths]

On 06/03/2024 at 14:55, Nickfromwales said:

 

 

@Russell griffiths got .28 on his DIY Nudura build iirc. That correct Bruce?

Yes I’m a bloody legend. 😂

[MikeSharp01]

Looking at our numbers and worrying about sizing our heatpump I cannot see a 5kW unit modulating down enough to manage a continuous delta of 5degC across our UFH a 3.5 kW might get close but is getting marginal on the DHW side of things. 

[JohnMo]

4 minutes ago, MikeSharp01 said:

Looking at our numbers and worrying about sizing our heatpump I cannot see a 5kW unit modulating down enough to manage a continuous delta of 5degC across our UFH a 3.5 kW might get close but is getting marginal on the DHW side of things. 

With my 6kW, I just batch charge the floor, I run my ASHP flat out, can run 7 hrs straight no issues. Have a target flow temp of 35, knowing it never get above 33 before the thermostat switches it off. Not the best CoP, good enough, on cheap rate, so still cheaper than gas.  Various ways to get around size issues.

[MikeSharp01]

8 hours ago, JohnMo said:

With my 6kW, I just batch charge the floor, I run my ASHP flat out, can run 7 hrs straight no issues. Have a target flow temp of 35, knowing it never get above 33 before the thermostat switches it off. Not the best CoP, good enough, on cheap rate, so still cheaper than gas.  Various ways to get around size issues.

Yes this is what @TerryEdoes only using Willis heaters. His decrement delay, like yours & ours I suspect, is very low so it matters not that we don't run the thing full time and anyway at some point we will need to put some of the the output into the DHW - which is now going to be a UVC (or some such water filled device) because I cannot get happy, given discussions here and elsewhere, with the Sunamp unit I had originally thought I would use.

 

Talking of DHW I have been wondering how best to control around that. We will have about 6kW of Solar so I am thinking I would want to top the UVC with that. Obviously the ASHP is the best thing to do that with, given the COP, so feed the ASHP with power from solar when the sun shines BUT once the ASHP reaches its max temperature switch over to the immersion heater fed by the Solar to give us some more stored energy. 

 

 

[JohnMo]

36 minutes ago, MikeSharp01 said:

Talking of DHW I have been wondering how best to control around that. We will have about 6kW of Solar so I am thinking I would want to top the UVC with that.

 

DHW, I tried various way to be smart, but found letting it sort its self out, worked best.

 

My heating regime is simple

Heat house and summer house first. This uses E7 and battery and solar if available, DHW is allowed to heat between 12.30pm and midnight via the ASHP. On a dull day heating DHW tends to be by ASHP, bright day like yesterday all DHW was heated by solar diverter.

 

Solar diverter to DHW only when the battery is charged from solar. This just picks up export via a CT clamp once battery charged.

[TerryE]

I entered this thanks to a poke from @MikeSharp01.  What @NailBiter is going through now is a journey that we started back in later 2013, with us moving into our new build in Dec 2017, a 3-storey passive-class (almost) house were we live on floors 0+1 and my son has bedsit style area in the warm loft on 2.  This is about a quarter of what NB is planning. 

 

We've been living in the place for over 6 years, and we are still amazed at how well it has all turned out in terms of performance as built against design expectation, and also in terms of its extreme durability and ease of maintenance.  We build on a split plot by selling the other ½ with its 17-19C stone farmhouse.  We saved a lot of money by doing a lot of the design, procurement and internal trades ourselves.  So the entire process was extremely profitable

 

My rule was only to take on tradework where our standard of build / finish would be at least as good as we could get from local tradesmen, and since we kept a very tight control on compliance and quality, the overall build standard is consistently high.   Overall we put in over 3 person-years of equivalent effort. This was a big percentage (effort and therefore saving) of a 230m² build, though it took us years to recover from putting in this effort and the general strain/stress.

 

Our sort of input just wouldn't dent a 1,200 m² build. You are going to have to rely on buying in at a realistic commercial rate a far larger percentage of trades and professional services.   Also guessing your extended family size, I suspect you have an expectation of a lifestyle,  per-person use and general quality of finish that is also on a different level from what most members here aim for.  I make this comment with no criticism intended, but more of a level-set from my experience and costs at 2015-2017 prices: my instinct is that you are at least 100% out on your budget expectations.  I would strongly suggest that you have the entire project plan and scope independently reviewed and costed by an experienced quantity surveyor: your overall project scope needs to be realistically matched to your finances, as there is not point in running out of cash with a half built project.

 

I have a few technical comments, but I will defer them to later posts.

[SteamyTea]

18 minutes ago, TerryE said:

my instinct is that you are at least 100% out on your budget expectations

And for half of the dream.

If the architect project manage it, that would be £200k.

 

[NailBiter]

15 hours ago, SteamyTea said:

And for half of the dream.

If the architect project manage it, that would be £200k.

 

You have the 2nd highest comment count in the thread but it seems you are focusing on quantity over quality. Can I please ask you again to go and troll somewhere else. I have no interest.

Edited March 9 by NailBiter

[ProDave]

On 08/03/2024 at 07:31, MikeSharp01 said:

Talking of DHW I have been wondering how best to control around that. We will have about 6kW of Solar so I am thinking I would want to top the UVC with that. Obviously the ASHP is the best thing to do that with, given the COP, so feed the ASHP with power from solar when the sun shines BUT once the ASHP reaches its max temperature switch over to the immersion heater fed by the Solar to give us some more stored energy. 

My "simple" way to achieve that is set the timer so the ASHP only starts to heat the DHW at 11AM, by which time there should be decent solar PV to be used up by the ASHP.

 

The PV diverter works automatically on it's own at any time, so on a sunny day the ASHP will be soaking up the PV and the diverter will be putting some into the immersion heater as well.

 

ASHP heats DHW to 48 degrees then stops.  Immersion heater thermostat is at maximum which seems to cut out just over 70 degrees.

 

5kW ASHP seems okay with low heating load and I would not want to go smaller for DHW heat up time.

[NailBiter]

16 hours ago, TerryE said:

I entered this thanks to a poke from @MikeSharp01.  What @NailBiter is going through now is a journey that we started back in later 2013, with us moving into our new build in Dec 2017, a 3-storey passive-class (almost) house were we live on floors 0+1 and my son has bedsit style area in the warm loft on 2.  This is about a quarter of what NB is planning. 

 

We've been living in the place for over 6 years, and we are still amazed at how well it has all turned out in terms of performance as built against design expectation, and also in terms of its extreme durability and ease of maintenance.  We build on a split plot by selling the other ½ with its 17-19C stone farmhouse.  We saved a lot of money by doing a lot of the design, procurement and internal trades ourselves.  So the entire process was extremely profitable

I'm very pleased for you (and your son!) that it has all worked out so nicely. Well done for all the hard work. Great to hear how quality craftsmanship / materials really do allow the creation of low maintenance buildings. That you managed to do it on a tight budget doing a lot of work yourselves is even more impressive. 
 

 

16 hours ago, TerryE said:

My rule was only to take on tradework where our standard of build / finish would be at least as good as we could get from local tradesmen, and since we kept a very tight control on compliance and quality, the overall build standard is consistently high.   Overall we put in over 3 person-years of equivalent effort. This was a big percentage (effort and therefore saving) of a 230m² build, though it took us years to recover from putting in this effort and the general strain/stress.

That's a good rule. I'd also add don't pay anyone to do something you enjoy doing or enjoy learning to do. Hard work does take a while to recover from but it is ever so satisfying, I bet you all enjoyed working together to create something so nice. We are reasonably young compared to most self builders so stiff upper lip time I suppose. From the sounds of your post you feel like you made the right decision.

Minus garages / workshop / gym and spaces that really don't need standard finishes we have about 600m2. We don't need all this space yet but we will grow into it as we need it.

I only get a VAT refund and CIL self build discount once. Demobilising / remobilising, inflation and economies of scale have a hand in my decision. As does the current geopolitical state of the world. Our globalised supply chains are fully functional right now. They weren't a few years back, will they be in a few years time? I'm striking whilst the iron is hot.
 

 

16 hours ago, TerryE said:

Our sort of input just wouldn't dent a 1,200 m² build. You are going to have to rely on buying in at a realistic commercial rate a far larger percentage of trades and professional services.   Also guessing your extended family size, I suspect you have an expectation of a lifestyle,  per-person use and general quality of finish that is also on a different level from what most members here aim for.  I make this comment with no criticism intended, but more of a level-set from my experience and costs at 2015-2017 prices: my instinct is that you are at least 100% out on your budget expectations.  I would strongly suggest that you have the entire project plan and scope independently reviewed and costed by an experienced quantity surveyor: your overall project scope needs to be realistically matched to your finances, as there is not point in running out of cash with a half built project.

I hear you and I appreciate you taking the time out your day to warn me against doing anything silly. I would however suggest that a 1,200 m2 build (particularly with the large ancillary spaces we have) is not 5x the effort of a 230m2 space.

We specifically designed our build to be geometrically simple and to avoid architectural fussiness. It is a great big rectangle which makes it simple to build. We also have perfect 360 degree access and plenty of room on site to store materials / equipment etc. This will make life easier.

I have a turnkey price here from a very fancy (I swear half their budget goes on brochures) construction management company. They reckon they can do it just shy of £3 million fully fitted out furniture and everything. I reckon they have a huge (40%) profit margin on that and that we can do it for £1.8 million fully fitted out. Of course however we don't need it fitted out to the standard they are suggesting nor do we need all the space yet. I value simplicity and size over fussiness.

The goal I've set (which I accept may be impossible) is to get the frame water tight / done inside of £1 million and get the majority of the first fix / some second fix done inside of 1.5 million. There is little point setting a target unless it is difficult to reach. I have every faith in our team, our family and myself. It helps that we ran a building company for years. We are not inexperienced and we have taken our time to use our knowledge to find the right people to work with. We also have the majority of the tools we need and knowledge of how to use them safely and efficiently. 
 

 

16 hours ago, TerryE said:

I have a few technical comments, but I will defer them to later posts.

I look forward to hearing these thanks for taking the time to write all this up.

Have a great weekend.

Cheers,

NB

 

Edited March 9 by NailBiter

[NailBiter]

19 minutes ago, ProDave said:

The PV diverter works automatically on it's own at any time, so on a sunny day the ASHP will be soaking up the PV and the diverter will be putting some into the immersion heater as well.

 

ASHP heats DHW to 48 degrees then stops.  Immersion heater thermostat is at maximum which seems to cut out just over 70 degrees.

 

5kW ASHP seems okay with low heating load and I would not want to go smaller for DHW heat up time.

Pardon my ignorance here but would the immersion heater (CoP of 1?) not be incredibly inefficient in comparison to the ASHP (CoP of 4 to 5)? Why not fire the extra juice from the panels directly into the ASHP and skip the immersion? Sure you'd have to upsize the ASHP slightly but would the efficiency gains not quite quickly pay for that? You can then use that energy for other purposes or even export it.

Edited March 9 by NailBiter

[ProDave]

7 minutes ago, NailBiter said:

Pardon my ignorance here but would the immersion heater (CoP of 1?) not be incredibly inefficient in comparison to the ASHP (CoP of 4 to 5)? Why not fire the extra juice from the panels directly into the ASHP and skip the immersion? Sure you'd have to upsize the ASHP slightly but would the efficiency gains not quite quickly pay for that? You can then use that energy for other purposes or even export it.

There is no easy way to command the ASHP to start up heating DHW when there is surplus PV, and in any case on a partly cloudy day PV production can go up and down in quantity very rapidly as clouds come and go.

 

Yes the immersion is a COP of 1, but the energy it is using if "free" and not using it, it gets exported and wasted (at best paid at a low export rate if you are able) so better to use it than lose it.  The PV diverter responds very quickly to peaks and troughs in the PV generation

[NailBiter]

3 minutes ago, ProDave said:

There is no easy way to command the ASHP to start up heating DHW when there is surplus PV, and in any case on a partly cloudy day PV production can go up and down in quantity very rapidly as clouds come and go.

 

Yes the immersion is a COP of 1, but the energy it is using if "free" and not using it, it gets exported and wasted (at best paid at a low export rate if you are able) so better to use it than lose it.  The PV diverter responds very quickly to peaks and troughs in the PV generation

What inverter are you using? You can normally get that info out of them but may need to use the serial port.

Apologies if this is common knowledge but I was unaware ASHPs took time to spool up. How long does it take?

Edited March 9 by NailBiter

[ProDave]

1 minute ago, NailBiter said:

What inverter are you using? You can normally get that info out of them but may need to use the serial port.

Apologies if this is common knowledge but I was unaware ASHPs took time to spool up. How long does it take?

My PV diverter measures generated and consumed power to that could "signal" the ASHP to start up if there was enough surplus, but that would then have to be integrated into the regular controls to override "DHW demand" regardless of what the time clock says.

 

Yes an ASHP takes a few minutes to ramp up, and they don't like starting and stopping so you really would not want to keep interrupting it every time a cloud came over.

 

I guess this is what battery storage does.  I don't have that on my present system, but later i hope to add more PV and battery storage.  Batteries should be ideally placed to soak up even short bursts of PV generation and then discharge the batteries later into a constant load device like the ASHP.

[saveasteading]

1 hour ago, NailBiter said:

go and troll somewhere else. I have no interest

...in anything that doesn't back up your own view.  I'll be off too then. I wish you well though, perhaps everyone is out of step except you.

 

[NailBiter]

Just now, saveasteading said:

...in anything that doesn't back up your own view.  I'll be off too then. I wish you well though, perhaps everyone is out of step except you.

 

You are welcome to participate, you are also welcome not to participate.

I'm not sure why but SteamyTea has decided he will sit on the sidelines and chuck in unhelpful comments. He has even stated clearly this is his intention twice in this thread. This is a waste of his time and our time.

If my politely asking him not to do that makes you not want to participate here I can only apologise and wish you well.

[saveasteading]

3 minutes ago, NailBiter said:

apologise and wish you well.

Calling a person a troll is not acceptable. 19,000 posts and 6 followers is not trolling.

 

[NailBiter]

Just now, saveasteading said:

Calling a person a troll is not acceptable. 19,000 posts and 6 followers is not trolling.

 

I think you misunderstood my comment, I used troll as a verb.

[TerryE]

By way of 2016-17 prices, our village plot was worth about £150-200K, bought-ins about £350K, labour and profession fees save by our contribution maybe another £120K giving an effective total of £650K which was about what roughly comparable houses were selling for in a village setting at the time.  OK, splitting the plot off probably lost us only about £50K off the selling price of our old farmhouse.  We have no CiL then and saved on stamp duties so probably saved ourselves maybe £250K on buying a "comparable" previously built house in the area. Except of course that you could buy a passive-class house and certainly not the exact spec that we wanted nor to the build standard that we actually achieved.  There were some major cost elements imposed by the LPA, e.g. local stone exterior skin, and natural slate roof, that added to our bought-ins.    At today's prices we would probably be looking at £750-800K to do a custom build to this spec.  

 

Can I suggest that it might be worth looking at an MBC twinwall TF build as an alternative to ICF at least for the main living space?  Their warm slab and TF design patterns have been well tuned to a passive-class standard over more than a decade's refinement.

 

I agree that if you've run your own building company, then you and whoever else in your family that worked in it will have lots of relevant experience, and you will have many areas of expertise in-house that you can either use directly or to enable a decent level of quality control.

 

One thing that many here evangelise is achieving a passive class build as this has major running cost savings, as well a far more comfortable living environment.  We are in our early 70s now, so we appreciate this as we age.  We keep our entire house at 21-23 °C (the first floor bedrooms are a couple of degrees cooler than the ground floor) 24 × 7, and really miss this when we visit our children and other relatives.

 

I personally would recommend that you or one of your close family really gets their head around the implications of building to passive class: where the heat goes and (through solar gain) where it comes in.  Relevant contributions of: slab losses, external walls, roof, fenestration, air exchanges.  Get a good feel for the impact of U values and how these reflect unit costs and performance; air-tightness and air exchange losses, and so on.  You will need to make various trade-offs to optimise costs vs achievement off your overall spec, and you or someone you really trust has to make these decisions.

 

Achieving this class of house requires an attention to detail both in design and in construction.  It is not unusual for two houses with the same nominal as-designed spec to vary in as-built performance by a factor of 2.  An example "close to home" is that my daughter's living room is impossible to heat economically: the large panel of bifold doors leading onto the garden have a poor U-value and leak terribly; areas of wall and ceiling insulation are missing.

 

You haven't mentioned your age, but I infer that you are getting close to retirement and therefore this will be your property "to retire into", so living comfort will be  important.  You've mentioned a gym and workshop but what you have mentioned in bridging space to the exterior: a conservation or atrium.  I am not talking about the 5 × 4m bolt on the side of an existing property, but in your case you have lots of area to include a decent spacious environment that to could properly integrate into the building fabric, and that could connect you to the garden.  OK, not needed in the summer where you are planning to build, but this could extend you comfortable "outside-ish" space for another 3-4 months of the year. 

 

BTW, even Nick (@SteamyTea) would admit to being a tad irascible at times; yes, he is also very particular about units, dimensions etc., because the implications of kW vs kWh, etc. are a lot more than a little "h". He is also well respected for his contributions here by the forum regulars.  🙂

 

Edited March 10 by TerryE

[Thorfun]

52 minutes ago, TerryE said:

Can I suggest that it might be worth looking at an MBC twinwall TF build as an alternative to ICF at least for the main living space?  Their warm slab and TF design patterns have been well tuned to a passive-class standard over more than a decade's refinement.

when I was looking at TF companies MBC wouldn't offer the warm slab as we were having a basement. they would've fitted their TF to the basement but weren't interested in the slab.

[TerryE]

@Thorfun, that's because their warm slab is an on-ground insulation-wrapped slab.  A warm basement is a completely different design requirement.

 

Edited March 10 by TerryE

[Thorfun]

8 hours ago, TerryE said:

@Thorfun, that's because their warm slab is an on-ground insulation-wrapped slab.  A warm basement is a completely different design requirement.

 

Agree, but the OP is having a basement and I thought I’d make him aware to set expectations before he went to MBC. 

[AliG]

Welcome,

 

I am probably one of the few people with a similar sized house on the forum.

 

I think this is quite a general discussion and if you want advice on anything specific such as ICF then it is probably best to create a specific post referencing that. This kind of intro post is likely to become quite rambling.

 

To some extent you are really building three houses which makes things more manageable, but I would not underestimate the costs and time require to maintain such a large building. I would maybe try and decide this within the family before going ahead. There is always something breaking, not working as expected, needing replaced etc. it takes up a lot of time and money. Think of the maintenance on 10 standard three bed houses. How will it be owned, costs apportioned etc.

 

My house is around 1000sq metres including the integral garage. It cost around £2m to build 8-6 years ago. We just finished a smaller house for my parents last year and it cost around twice as much per square metre. I would be quite concerned that your budget is low and already seems tight. In my experience I got constant questions from the architect and builder over the course of construction. The questions always went along the lines of we can do A that costs X or B that costs 2X. 9/10 B was the right decision. It would get very stressful if the budget was tight.

[Carly Lawson]

Hi, that sounds like an amazing build.  We looked at Nudura but then we found out you have to use loads of bracing and extra bits, which is very expensive and not included in the price, we also worried that the render may not stay on. Plus we are trying to be as environmentally and sustainable. We found out that Nudura is imported all the way from America?  

We are still trying to decide which product to use for our self build. We looked through your post and we have also looked at Durisol/Ecobrix because you mentioned them. We did some research and thought that it looked like a better option as it's more straight forward no extra costs and UK made.

 

We saw them at them at the NEC show. They invited us to visit one of their builds and they gave some history about the product. We were amazed that Europe has more than 400,000 houses built with woodcrete and that its been around for so long.