Iceverge

A few more pics if the room as is would help. I think to get any satisfactory result you"ll need to move the radiator and raise the sill of the window at a minimum.

Ah yes. Can you get to 150mm as a minimal. The. 175mm, 185mm and 210mm on the other areas to make it level. I expect you'll have joints anyway at the doorways so this should take care of any differential movement. If you are worried about cracking in the middle of the room you could use 70mm concrete with 10mm chip and plasticiser with some steel mesh powerfloated to finish.

You have a total of 25mm for insulation or 25mm difference?

No issues. Just use the Maxim amount of insulation you can. How much depth do you have to make up?

I would say it'd be prudent to block the top of the cavity to prevent any EPS beads escaping if you full fill it later. From a fire point of view it would preferable too. I would stay away from PIR between the rafters and use a 50mm mineral wool or woodfiber batt and then more insulation below the rafters. Something like Rockwool Flexi or steico flex. Woodfiber is particularly good for summer overheating protection. Ease of fitment, noise, heat protection, fire, cost, thermal drift, are areas that PIR doesn't cover itself in glory.

Easy with rads and TMV I assume?

Yes you're right. If you add grid losses at about 7-8% into it where do we end up?

Wrap the whole building in plastic in situ. Guttering, slates, birds nests the lot . Nothing too technical, maybe like that black stuff they put on pallets, or bales of grass silage. It should be reasonably durable once out of the sunlight. Erect a 4 post portal frame outside it with a metal pitched roof. Then wrap the frame in some of that cement impregnated fabric they use for military huts and canal reinforcement. Wait for a rainshower to allow it to set .Then pump the void in between with EPS beads. Exhaust source heat pump for DHW and ventilation and A2A for heating. Windows and doors optional.

Tying it to m² has little benefit I would argue, just more unnecessary complication. The vehicular analogy would be an "A" rated lorry @ 10MPG or 0.0025Gallon/Mile/Tonne Vs a "B" rated hatchback at 50MPG or 0.013Gallon/Mile/Tonne. Twenty times worse on the face of it. The EPC rating for houses gives the impression that if we all drive efficient 18-wheelers our problems will go away. In fact it promotes the building of larger houses as on a per m² basis as they're easier to achieve a low kWh/m2/annum than smaller houses. This will increase overall energy use. Adding solar production to balance high winter losses caused by poor building fabric exacerbates emissions until we have some viable interseasonal energy store. Take house 1, a glass masterpiece with poor form factor and average glazing etc. Uses 10000kWh per annum for space heating but thanks to a generous solar array generates 8000kWh in the summer. House 2 has no PV but is super insulated. 2000kWh/ year space heating. They have the same EPC rating but there is an 8000kWh difference in bought in winter electricity say at 50% fossil fuels means the solar PV house would use 4000kWh more of FF energy. Bonkers. Houses should be rated at kWh/annum in my opinion. Keep renewables out of it and offer proper feed in tariffs for that part of the game. Similarly specific heat demands out if the picture. It's counter productive.

It's bonkers complicated. How about kWh/year. Much like MPG for a car. At the moment an enormous house with average heat loss but with a deathstar worth of PV on the roof can be A rated. It'll still cost a fortune to heat in the winter.

The UK has historically been a strong economy globally, GDP per capita was high and the cost of energy was relatively modest on an individual's pocket. When I lived there I was always surprised at how terrible house windows and doors were. Drafty sash single glazed items with solid timber frames from the early 20th century were the norm. They all disappeared in Ireland in the 1990's replaced by not so pretty but vastly thermally superior PVC double glazing. I suspect it was because we had no money then and couldn't afford to heat our houses otherwise.

@RichardL like you I think A2A is a sensible option, even for for old properties. @Hanksy did a few posts a year or two back demonstrating this. Unlike ASHP you avoid heating any fabric (UFH) which in uninsulated houses is a black hole for energy use. A good unit can be installed for maybe £1500. One in the hallway or living room of every gas boilered house could significantly reduce gas demand (provided the power stations run on something low emission) . Minimal disruption Vs ASHP and better COP. Leave the gas in place for topping up cold rooms and DHW.

70mm screed 100mm insulation 25mm sand blinding 125mm concrete slab (with A252 mesh) How about. ( With your SE's approval) 100mm concrete slab with mesh Slip membrane 300mm eps/200mm PIR DPM This is what the builder did on ours.

Yes, I'll replace it with something like OSB soon I think. My logic was that there will be so much airflow through it that all small particles and off gassing will get done pretty quickly and become inert .

I think the idea that if you design it well and insulate it sufficiently then you can run it at very low flow temps. That means that if the floor is at 25⁰ and the room is already at 25⁰ due to sunlight/woodburner whatever then the water passes through the UFH in that area without actually emitting any energy. It'll give proportionately more energy to colder rooms than warmer ones. Hence no zones. This won't work with high temp rads at 70⁰ for example as they'll still emit heat as the room will always be colder.

We had an airtightness of 0.32ACH which was bout 4900mm2 of open area over 600m2 of envelope. A glance at some ventilation charts suggests 550mm2 per kW of installed appliance so even in our house we would be able to have a 8.9kW appliance. A CO detector is still a good idea in case of a blocked flue etc but I wouldn't worry in the slightest about the ventilation in your case.

Bought Amtico from ebay and stuck it down myself. It needs to be super flat so SLC is a must I think. It's only been 2 years but I suspect it'll last until the next ice age. We also have some click fit LVT from Pergo, oak effect, fitted floating not glued. Much simpler to fit but nowhere as tough as the Amtico. Also floating wouldn't be my choice again as it has bubbled slightly in 2 of the rooms. It is far warmer underfoot than normal tiles and substantially more forgiving for children falling and dropped plates etc.

‘The field tests show that a siloxane impregnation, if properly applied, can repel rain water to such an extent that a complete drying of the masonry is possible… It seems possible that inappropriate impregnation can even increase the moisture content and hence the danger of frost damage… The quality of workmanship and the preparation of the façade, for example by repointing it, appear to be of major importance. If the quality conditions are met, an impregnation can be considered as an effective rain protection. ‘The field tests show that a siloxane impregnation, if properly applied, can repel rain water to such an extent that a complete drying of the masonry is possible… It seems possible that inappropriate impregnation can even increase the moisture content and hence the danger of frost damage… The quality of workmanship and the preparation of the façade, for example by repointing it, appear to be of major importance. If the quality conditions are met, an impregnation can be considered as an effective rain protection. Small cracks up to 1mm do not affect the rain protection if they are thoroughly impregnated and if the walls if of sufficiently low air permeability, e.g. by the application of a plaster on the inside.’ Künzel & Kieszl (1996) This suggests if done well it is a valuable addition.

Sounds like the most fire safe house on the planet. Is that a brush on or spray? Did you rate it?

Welcome welcome. Any chance of a plan sketch of what you'd like. Maybe some photos too of the similar styles that take your fancy.

This might be easier to build. Note the 50mm insulation outside the concrete, the 50x100mm wall plate supporting 150mm studs to give a much better junction thermally. Something like EPS 100 should be fine for a garden room. I've thickened the slab 50mm at the edge for some strength but it's educated guesswork really. Some reinforcing mesh would make it much stronger too.

Stolen quote from a different thread. Doing the sums: Based on an installed cost of €6000 for an ASHP and UFH and €2000 for a WILLIS and UFH Our space heating of 2500kWh/annum (COP of 4 for the ASHP) DHW of 3200kWh ( COP of 2.5 for the ASHP) Day rate of 48c/kWH and Night rate of 14c/kWh then the total 7 year cost of €7831 for the ASHP and €7,666 for the Willis. Assuming zero maintenance for both. With double the space heating (5000kWh) the sums are €2k in the ASHP favour. Except for the cooling I don't think there's a case for ASHP in low heat demand houses. Maybe the transition from ASHP to Willis is a good marker for how passive is passive enough. Even with our current system of direct electric rads the 7 year cost is €8603. Swap out for a good A2A @ €2000 installed cost and the cost drops to €6,374. Any recommendations, for what brands? We have a fused spur in the bathroom + ensuite crying out for exploitation.

I would say an experienced a oak timber framer would be worth a consultation before committing to a design. One of the projects I linked had £6000/m2 cost and that's pre 2020's inflation. Oak etc get proportionally much more expensive as it gets thicker and longer. It could easily save you a 5 figure sum to have some pre planning advice from someone in the know.

With that in mind I would propose the following. FLOOR: 50mm PIR to the floor ( or as much as possible) 2 x 11mm layers of OSB staggered, glued and screwed) WALLS: 75mm Cavity wall mineral wool slabs to external walls between 50mm X 50mm battens at 600 centres stood off the wall by 25mm spacers. Variable diffusion membrane to the inside like Siga Majrex 200 or Intello Plus. Taped very diligently to all penetrations, roof and floor and returned at least 300mm to all internal walls. It's important this has ZERO holes. All wires etc should be in the service cavity or taped completely airtight. 20mm service cavity with battens ( or resilient bars) at 90 deg to wall battens for service cavity. 12.5mm plasterboard CEILING: 75mm mineral wool batts placed across the rafters between battens to maintains 75mm ventilation above. 20mm service cavity as above. 2 x layers of 12.5mm plasterboard for noise. Obviously the suggested insulation values are only notional and more is always better. For ventilation a small MVHR unit like this would do the trick. As it's gym you probably wouldn't need any heating.

From a structural and safety point of view you always need to consider the effects of moisture on a building. Firstly external moisture. This is easier to visualise. 1. Make sure the roof isn't leaking, valleys chimneys etc. 2. Make sure that gutters are all working and taking water away from the building. 3. Make sure no water is pooling by the external walls, correct sloping/french drains can solve this. 4. Make sure that the water table isn't trying to push water up through the floor, again a french drain is a great and cheap way to solve this. Secondly internal generated moisture. Tougher to see as it's largely water vapour from breathing/cooking/showering drying clothes etc. It stays as suspended tiny moisture droplets in the air and forms into water droplets when it gets cold. Much like steam from a kettle condensing on a single glazed window. This is a real problem in almost all houses as it is hard to see and it's poorly understood. The consequences , mould, rot, damp and smells are widely known however. The air can suspend a certain amount of water vapour particles per m3 depending on temperature. At 4 deg it can hold 6.4g of water vapour per m3 of air. This is the maximum and is called 100% relative humidity (RH). You will see this as fog outside. However if you bring that m3 of air inside the house and heat it up to 20 deg it can hold much more moisture, 17.3g/m3. Given that it only has the 6.4g, that means it is nowhere near it's capacity to hold water. It's absolute humidity ( 6.4/m3) is the same but its RH has dropped to 37%. This is why weirdly if you open the windows and doors briefly on a foggy day, let in 100%RH air, close the doors, allow the air to heat up it'll really aid the drying of the house as it can take on much more moisture. A similar thought experiment can be done in reverse. Take your kitchen RH 70% and 20deg. That is 12.2g/m3 in absolute humidity. Unfortunately you have a poorly insulated window where the surface temperature is 12deg. The air that touches this gets cooled and it's RH climbs to 100% at 14deg. This is called the dew point as it is where dew begins to form. As the temperature of the air beside the window continues to drop the water vapour has nowhere to go and condenses out of the air making droplets on the window making an area for mould and damp. Not a massive problem if the window is in a breezy area of the house where it can dry when the RH drops again but a real issue where air movement is limited like behind furniture etc. The solutions for this are four fold. First ensure you have proper ventilation. It needs to be forced and continuous. Trickle vents and hole in the wall vents do nothing in still weather and too much in windy weather. This will take the internal air and replace it with external air that can help keep the house dry more. This was the a job of the fireplace in ye olde houses and mechanical ventilation in new ones. Secondly, build your house in such a way that no internal surface gets cold enough to collect condensation. This is typically a surface temperature of 16 deg for most houses. It can be easily achieved in a solid walled building by just running the heating a lot. A better way is to add a continuous layer of insulation. Thirdly, you need to do your utmost to prevent any moist internal air from getting into the structure of the house via cracks, holes and incomplete construction. Thirdly, keep the damp air out of the structure of the house where it could condense. This is done with a good airtightness layer. Fourthly you need to ensure that any moisture that gets into your structure can dry out as quickly and painlessly as possible again. Vapour open construction is best. I hope that wasn't too much theory. TLDR Deal with bulk water from outside, it's easy to see and solve. Then deal with damp caused from inside via 1. Ventilation. 2. Continuous insulation 3. Airtightness 4. Vapour open construction.