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Some design strategies please


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Ok treat me kindly I’m new and I need to do a bit more reading as I’m getting confused  😂 

the self build I’m doing will be approx 160m2 over two floors and will be built highly insulated and airtight ( without going for the passiv certificate) . 
I guess what  I need to know are what I my best options for 

1 heating the underfloor heating 

2 ventilation of the house 

3 hot water

 

4 there will be a solar system option with battery and also need to know best option for the electric supply to the property.

 

we are only 3 permanent adult in the two bed house normal electrical demands 

 

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Hello and welcome

 

1. ASHP with cooling capability, run through UFH. Flow temps will be low so CoP from heat pump will be good and cost less than most other heating options.

2. MVHR

3. ASHP (same as 1.) UVC with 3m2 coil

4. Connect to mains power via your local electric supplier.

 

Keep everything as simple as possible, UFH you don't need zones a single zone, will allow you to eliminate the buffer and additional pump, no need for wiring centre or manifold actuators.

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CoP or coefficient of performance. Is basically how many units of heat you get, for how many units of electricity you supply.

 

So a CoP of 3 is one unit of electricity and 3 units of heat. The lower the difference between outside air temp and the water heating temp the better the CoP. So heating water to to 25 degs yields a better CoP than heating to 50 degs.

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1 hour ago, Nic said:

will be built highly insulated and airtight

Have you some numbers for these.

Building regulations are a minimum requirement, and really quite genetic.

One big area is floor insulation with UFH. Thermal energy can easily be conducted to the ground i.e. wasted.

 

Another area is PV on a roof. Most people will tell you that there is not enough in winter, too much in summer. While true for our latitude, steeper, south facing PV array can improve the usefulness.

Batteries are all the rage, but you can buy just the right amount of power at under 40p/kWh, which is really quite cheap when you think about it. And you can do that exactly when you need it.

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Early stages of a first self build for next year , so no figures yet . Looking at the Durisol ICF 365 blocks for the build which has 165 mm insulation and 120 concrete. Will of course insulate under the slab ( not sure what is recommended here) and then a warm roof ( again unsure of insulation at this time ) 

 

thanks again 

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Welcome. Good advice above.

 

When using ufh there are other advantages: warm feet make us feel good, so the air temperature ( air heated from the floor) can be lower than the norm (tell people it is 20°t though.)

So the air isn't so warm  and there is energy less wastage when doors are opened.

I don't agree about the single zone, as some rooms can be cooler.

As @ProDave says, upstairs bedrooms may not need heating at all.

As all your space heating is from the floor, this needs lots of insulation, not forgetting horizontally to the outer walls.

No carpets, or get special ones that let heat through. Ceramic tiles are best.

 

Because of the CoP, the rating of the air source heat pump (ASHP) is the output, and the electric supply is 1/4 or 1/5 of that,  hence a normal mains supply is enough.

 

Structure....what would you like? Then it can be made to work.

 

I could never get ICF to work out commercially, but many swear by them and I can see the attraction for DIY.

 

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I like the idea of Durisol over the other ICF systems because render and stone slips can be applied directly to the surface on the outside saving time and money ( those who I have seen that have used it have liked it a lot) also again internally there is no need to plasterboard the surface it can wet plastered straight to the surface . Again saving time and materials 

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That's fine. With render I can see that is an advantage. Its just that, with the systems I looked at, it always ended up a much higher quote than the marketing had implied. 

Also I seem to recall that it wasn't great for large rooms, but others on here know more as they have done it.

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We used Durisol, would use again.  365mm will give you a wall with a U value of 0.14, but only if you include a service void, if the plaster direct the U valve falls slightly. Do not get a normal builder to build with Durisol there is a high probability he/she will balls it up, the corners especially. You can screw things directly to Durisol (with the right screws) such as service battens.  A service void make plumbing and electrics easy, otherwise you have to recess them.  Durisol is very abrasive, so will wear cutting tools quickly. 

 

You have to read and follow the build manual, once you start pouring the concrete there is no second chances. Concrete used as like water when it goes in, you cannot use vibrating tools to help compact, hence the water like consistency, the water open nature of the Durisol structure allows the concrete to naturally dewater.  You will need to factor in several concrete pours and possibly cement pump hires as you fill with concrete every 6 layers (1.5m or so). Have the architect design the flow of the building around the size of the blocks (corner to corner length, corner to window opening etc) and don't have too many corners (unlike our house).

 

Airtightness - Durisol is not airtight or water tight - advantage and disadvantage.  You have to know where your airtightness layer will be and it has to be continuous, so something to think about. Mine was inside so a could make the roof structure airtight inside also.  So I parge coated the inside, but you also need to seal the floor the wall junction and roof to wall junction and around window/door returns. My parge coat was a concrete/lime mix and wall remains breathable. 

 

Some food for thought

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2 minutes ago, JohnMo said:

hence the water like consistency, 

Presumably they specify a plasticiser additive and a small aggregate mix. This provides very much better strength quality than added water.

 

When you have the 6 course constraint, does this result in lots of small deliveries of concrete?

 

 

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41 minutes ago, saveasteading said:

Presumably they specify a plasticiser additive and a small aggregate mix. This provides very much better strength quality than added water.

 

When you have the 6 course constraint, does this result in lots of small deliveries of concrete?

 

 

No plasticiser, less than 10mm (I think) aggregate, very high slump. The water basically drains away.

 

We had 2 deliveries of concrete, plus a batch mixer for about 4 hours (for a part fill of Durisol by bucket and several other concreting jobs around site) and 2 hires of cement pump.

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5 minutes ago, SteamyTea said:

Does it need a curing retarder in the mix?

Not that was specified by Durisol or structural engineer.

 

I was was pouring in December so plenty cold enough.

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44 minutes ago, JohnMo said:

The water basically drains away.

 

Interesting.  The water drains away but without taking cement with it, ie the blocks act like a filter?

 

That could still leave more water in the mix than the theoretical optimum, but perhaps that doesn't matter as it is filling voids, not the entire structure.

 

Entirely for my curiosity, could you theoretically be laying blocks,  with another person mixing concrete on site and following behind? None of the excitement of whether it will hold when the big pour goes in.

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4 minutes ago, saveasteading said:

The water drains away but without taking cement with it, ie the blocks act like a filter

Yes it funny to watch, grey slug goes in the top, clear water out the bottom.

 

The structure of the blocks and the resulting concrete shape, is like a lattice structure, not a solid chuck of concrete like polystyrene ICF.

 

9 minutes ago, saveasteading said:

could you theoretically be laying blocks,  with another person mixing concrete on site and following behind?

Don't see any reason not too. We had had some very small sections of wall between doors and corners so these were filled by buckets, so as not to move anything with the pressure of a cement pump.

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17 minutes ago, saveasteading said:

Entirely for my curiosity, could you theoretically be laying blocks,  with another person mixing concrete on site and following behind? None of the excitement of whether it will hold when the big pour goes in.

Or making shuttering to hold the inconsistently shaped blocks in place.

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Airtightness - Durisol is not airtight or water tight - advantage and disadvantage.  You have to know where your airtightness layer will be and it has to be continuous, so something to think about. Mine was inside so a could make the roof structure airtight inside also.  So I parge coated the inside, but you also need to seal the floor the wall junction and roof to wall junction and around window/door returns. My parge coat was a concrete/lime mix and wall remains breathable. 
 

@JohnMo

would be interested if you could expand on this a bit more with details of how you made it airtight with the details of what was used . Also did you do a service void on all walls was that just a batten and plastic board what size voids did you go for and did you fill it with anything? 
cheers 

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5 hours ago, Nic said:

I like the idea of Durisol over the other ICF systems because render and stone slips can be applied directly to the surface on the outside saving time and money ( those who I have seen that have used it have liked it a lot) also again internally there is no need to plasterboard the surface it can wet plastered straight to the surface . Again saving time and materials 

 

Have a look at Velox ICF which also uses woodcrete and is also now available in large panels (4 x 3 metres)

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2 hours ago, Nic said:

would be interested if you could expand on this a bit more with details of how you made it airtight with the details of what was used . Also did you do a service void on all walls was that just a batten and plastic board what size voids did you go for and did you fill it with anything? 
cheers 

Parge coat was a double cream consistency mix of cement, lime and soft building sand. Mix was applied with a soft broom, just enough to fill the gaps in the block surface. I used 50mm square battens, screwed through the parge coat into Durisol block. I used a CT1 sealant at the point where the screw broke through the batten to help seal.

 

I used airtight paint at the floor wall junction. On the wall to roof junction I draped the avcl membrane down the wall 150mm and used airtight sealant to seal to wall.

 

Some photos 

 

IMG_20210615_084343.thumb.jpg.129d1cef28012db491e561994998cddb.jpgScreenshot_20220716-084356.thumb.jpg.f8382caede81ccd547cf9be7f3e13e20.jpg

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@JohnMo this is really helpful thank you. I take it you just plasterboarded after ? Did you use any additional insulation for 50mm void ? Was this a warm roof design? 
thanks. Again 

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