Smallholdertoo

Thanks for the comments and the support. The SE is yet to confirm the thickness though he has mentioned 250mm in the past. If it does turn out to be 250mm any thoughts how to persuade him to let it be thinner? Its probably worth mentioning that in readiness for the build we have installed 11kw of PVs and 20kw of battery storage on a new shed. This will provide the power to the new house. would this affect your choice of ASHP

We are due to build a small very well insulated 1.5 storey timber frame house later this summer. Using the Jeremy Harris spreadsheet, the house will have a thermal demand of under under 2kw when it is -10c outside . U values of 0.09, 0.13 and 0.10 for the roof, walls and floor respectively. The house has passed Part O for overheating and will have MVHR. We are now definitely going to have an85m2 insulated reinforced raft. I want to have ufh in the raft and in line with what others have done on this site it will have 3-4 loops, a singe zone and one thermostat. We will have a small ashp perhaps 3.5-5kw. I expect water temperatures in the ufh will be under 25c. The ashp will also provide our hot water - a 250l unvented cylinder. I keep on being given the advice that a 250mm slab will be very slow to heat or cool e.g. from my designer "My concern with a heated slab of 250mm thick is that the response times will be so slow that you will find that you are unable to adjust internal temperatures when the house heats up to the required temperature and then continues to heat when you don't want it because of the thermal mass." I am aware that the raft will be slow to warm up and cool down but am I right to believe that with the weather compensation a single thermostat and a low water temperature I am unlikely to have the issues suggested re overshoot? It would be great to hear from those on the forum that have thick rafts, ufh in raft and a well insulated house . Thanks in advance

Thanks everyone for your comments. I have just spoken to the TF company and they confirm only the internal stud needs to be on the slab, the rest 160mm can be supported by the insulation. So we will be going insulated structural raft route.

We are due to build a 130m2 near passiv house timber framed 1.5 storey house with a brick plinth in the early summer. We decided to go larsen truss timber frame I was hoping to have a highly insulated structural raft (u-value .10) with UFH in the raft but now my designer has been informed by the SE that the larsen truss will be structural both on the outside and and inside studs so will need to be fully supported, He had initially assumed that only the internal stud would be structural which would have allowed the non structural outside stud to cover the insulation between the brick plinth and the slab. This change produces a cold bridge as shown below in blue. He is now suggesting that we should go with strip or trench foundations and a slab as shown in the drawings below. I am concerned that there will be cold bridging and a u-value of.10 may not be achievable. Any thoughts on his suggestions and how they can be improved or how we can still use a insulated raft?

We didn't need to use British Gas as when Octopus rang, we explained that National Grid should be fitting the supply on the 12th of December. The man from Octopus replied that there was an appointment for the 13th if that would work for us. So hopefully we should have a supply in 3 weeks. Thanks for your help Sometimes I just worry too much!

What was the lead time when you put in the order to when the meter was installed?

Our 3 phase 42kVa supply is due to be installed on 12th December. It is to be installed in a new stable shed but will power our new annexe when it is built. On contacting Octopus I was told it will be more than 4 weeks before the smart meter can be fitted. I will find out the first available fitting date tomorrow. I believe that when you swap electricity suppliers you now do not need a new smart meter. I guess, I could get one of the other other electricity suppliers to fit the meter and then swap to Octopus once meter installed (and new PVs are on the roof). My question is - Does anyone know of other suppliers that are quicker to install 3 phase smart meters ? Thanks for your help, in advance.

@nod What are the main causes of the damage? - contact with the Power float, scuff damage from boots etc. and how to best avoid if determined to have UFH pipes in the concrete slab ?

Many thanks for your responses - Luckily the concrete will not be the finished floor. We will be tiling over it! Are you aware of any youtube videos that show this?

As this is something I have never done, does shuttering off the area work for a reinforced raft? The drain will be at an edge rather than the middle. How did you do yours?

I guess the intention will be to tie the pipe to the rebar that will be 200mm apart. Would it help if the manifold was pressurised with water? I accept it will be slow to change temperature . Thanks for your comments.

Agreed wellies are unlikely to damage the pipe. Thickness not yet finalised SE has yet to do soil analysis but 250mm has been mentioned. Wet room issue relates to how to plan for appropriate falls in the downstairs wet room to ensure that water runs to the drain.. Screeding feels like it may be better for adjusting levels in a small area. If I'm honest I haven't a clue how to address the drainage of the wet room. Suggestions welcome!

We are finalising the plans of a one and a half storey house (c.90m2 footprint). This will be well insulated -with u-values of walls .12, roof .10 and the insulated structural raft 0.10. It will have MVHR, so should have a heat requirement of around 2kw even when -10celcius outside. I suggested to the SE that UFH pipe would be within the power floated structural raft and this was his response "I am apprehensive about this detail as there are several risks including damage to the system during pouring of the raft and the requirement to maintain sufficient cover to the reinforcement. I suggest that the more conventional screed-based systems may be more suitable and would likely make the detailing of wet rooms etc. easier." I would still like to go this route. I am not convinced that there be any material increase in risk from having the pipe in pumped concrete as compare with a pumped liquid screed. Any damage is more likely to come from hobnail boots than the concrete. and in regards to his comment re coverage, this could easily be addressed by increasing the depth of the slab by 25mm. This cost of 2m3 extra concrete is tiny compared with the hassle and cost of 60mm of screed. I accept his point re the wet room. I am unsure how to address this other than having shuttering to reduce the height of the concrete where the wet room is and screed to hive required levels. Any thoughts how should I respond.

We have permission for a small 1.5 floor house. This is due to have some green oak framing internally (not structural) and an external oak framed door with a fixed triple glazed pane ether side. I want the house to be well insulated and airtight. I am therefore getting a bit twitchy about the green oak and am wondering whether I could use oak glulam instead as it would then be possible to glaze using aluclad softwood windows and door frames within the glulam frame to match the other windows. Yes i would lose some light but I would have less hassle in the longer term and better thermal efficiency. Any thoughts on the concept and who I should get to do the work? The frame is 2.7m long and 2.1m high. Has anyone done anything similar?

Thanks I will!