smart51

I think it worth giving a few more details. It is a suburban site that once housed two buildings. The larger of them was demolished over 20 years ago. The smaller building remains. We would build a house and I would keep the current building as a workshop. The site was split in two a little over 20 years ago. The other part was given planning permission and 6 bungalows were built on it.

£100/m2 but a lot of m2. It is almost the same price as the surrounding houses.

I know what you mean, but... We've been looking for a plot in the area for years. One has been to auction twice but withdrawn the day before both times over disputes over ownership. One was a tiny patch of car park between a shop and a prison. The other was a triangular scrap of land between the back of a hospital and the railway line. I'd like to make it work, but I wonder if it is adding up to too much trouble.

I'm not sure what you're saying. We are looking at a plot which is for sale with an advertised guide price. The firm of surveyors handing the sale has sent us a form where we make our offer together with any due diligence conditions that our offer may be based on. They sent us to a link to some documents which include site plans. The plot is advertised on Rightmove and that's where I found the brochure. Buried in that is the Overage statement. We want the site to build a single house for ourselves. You could fit 8 terraced houses on it at a push. What would the seller state when applying for outline planning permission? It is a less than ideal situation. I'd like to navigate through it as best as possible.

We're making enquiries into buying a plot. I've noticed that tucked away on the brochure there is a clause "The vendor reserves the right to receive a future Overage being a percentage of the net increase in value created by planning consent over and above the base purchase price or part thereof". Why might they not just state that they want an overage and state the terms? Could it be that it is a way of jacking up the price if the offers received are quite low? I've checked the list of planning applications for the site. There is nothing in the last 20 years and nothing was rejected in the whole history of the site, so it's not that they've applied for planning and been refused. Is overage only usually applied if the land is sold (within the specified time). So if the value goes up with planning permission but you keep it, no overage is payable?

On balance I think it wise to fit a heating system and use the ASHP to heat it. Underfloor heating it is, but with pipes fitted at generous intervals.

The house is single story and the roof will overhang the south facing windows by 2.5m . In the summer months, no direct sunlight will get in through the windows, save for early in the morning.

Air source heat pump, which of course could do heating. Heating demand would be 10W/m2 with a 30°C temperature difference. I suppose a very sparsely laid out UFH would save a little bit of cost. Since typing the question, I realise I'd forgotten to calculate solar gain. The southern wall is entirely glass. On a sunny winter solstice, that could be worth 3.6kW averaged over 24 hours. Even a cloudy day could be enough, which is probably the point of passiv haus!

I've been getting online quotes for windows and doors and notice that it is not much more expensive to go for windows with a centre pane U value of 0.6. For larger units, that yields a whole window U value of about 0.11 which is impressively good. 200mm carbon filled EPS gives walls with a U value of 0.15, plus floors and ceilings need to be 0.13 anyway. This takes us into passiv haus territory. With new build airtightness and MHRV set to give 0.3 ACH, we're looking at a total heating demand of 1.5kW to maintain 20°C above outside temperature or 2.2kW to maintain 30°C above outside temperature. Clearly we need some heating but not much. Under floor heating seems a bit overkill. What is a sensible way to provide this?

I suspect it is the void between the roof and the ceiling that silences the rain. Nice looking house BTW.

What would you suggest is more realistic?

I'm planning a new build that will have a flat roof with something like an 8° pitch. I want to avoid it being noisy. We currently have a loft conversion. The roof is made of 175mm timbers with a plywood deck and EDPM covering, plasterboard underneath and foam board insulation between. Birds walking across the top are loud and so is rain. I guess the whole think is like a drum skin. How do you make flat rooves quiet? My guess would be that pitched rooves have separate timbers supporting the tiles and the ceiling. Two sets of timbers sound expensive. What are people's experiences with posi-joists? Are they equally noisy or do they acoustically separate the plaster board from the roof deck?

That all makes sense. Features, materials and finishes. Large spanned open spaces cost more in joists than normal sized rooms with supporting walls. Slate costs more than tile. Shadow gaps cost more than skirting and architrave. That's a useful insight when playing with ideas.

A pavilion has an outside terrace with an overhanging roof, usually on the south side to shield the sun from the windows. Rather than going full Mies Van Der Rohe and have a frameless glass wall dividing the terrace from the open plan space in the house, we'll be going for full length bifolds, which is the modern equivalent. Otherwise, steal away. That's kind of the question I'm trying to answer. Is high spec all metre square porcelain tiles and unobtainium worktops with slate feature walls and frameless windows, or is it anything above what you'd buy in B&Q? I'm not interested in shadow gaps and skirtingboardless junctions really.

After years of looking, we've found a self build plot. It's not ours yet, but I'm putting a lot of thought into build costs etc so that we've got a plan. One of the things I've not nailed down is an outline price per m2. Various places say £1500 to £2000 m2 for a medium finish and £2500+ for a high end finish. Nowhere spells out what they are though. We're planning 200m2 of single story pavilion style house. Brick and block, flat roof (circa 8° slope) with 30kW of PV. under floor heating, heat pump. Painted plaster internal walls. Nice bathrooms (two off) but not extravagant. High Street kitchen. 50m2 kitchen / diner / lounge with bifolds. Aluminium windows. Where does that kind of spec land us? Nicer than a new build 3 bed semi but no where near Grand Designs.

We're going to put an offer in on a 1930s detached house tomorrow. The house is going to best and final offer this week. The plan is to insulate and extend. 2 years of looking for a self build plot has been 100% unsuccessful and this is the next best thing. We have MHRV on our current house and it does seem to work, certainly when it is on boost. The think is it is noisy. Even though it is in a cupboard in the converted loft, you can hear the hum upstairs when everything is quiet at night. In the loft bedroom you can hear it in the day time too. We're going to fit new windows throughout, external wall insulation, underfloor insulation. We're going to have an air source heat pump and underfloor heating. We want the house to be as low energy as we can practically do. But we're not going to strip off the plaster or seal up every crack. There will be no taped up plastic sheets in the walls keeping the house airtight. Given the 'good but not perfect' fabric of the building, is MHRV going to have a useful effect on energy consumption that is worth the effort of putting the ducting in?

I'm drawn to using white clay bricks, for example like a caxton ghost white. I've seen white bricks in North Yorkshire when driving past them but never stopped to get out and look. My concern is with how clean they stay. I want a zero maintenance surface really, like your average red brick.

In service or just during construction?

I must be reading this wrong. Thermalite Turbo aircrete blocks have a quoted insulation value of 0.11 W/m.K according to the data sheet. Part L for England (2022) calls for 0.16 for walls and 0.11 for floors. At face value, it suggests that a single skin of blocks is enough. What have I got wrong? Is it per metre thickness of Thermalite block, rather than for 1 block thickness? https://www.forterra.co.uk/wp-content/uploads/2021/02/Thermalite_A5_guide_2020.pdf

Internal floor space? I'd assumed external foot print, so including the external walls. If I have to build a single storey, there's about 10% difference, slightly more at two stories. I like errors in my favour.

There is a plot of land up for auction that we have our eye on. It is between back gardens and allotments. My concern is that the council might impose a height limit on any development which would mean a single story building. Before we get in too deep, I want to know what that might cost. There is enough room to do what we want with a single story building but I'd prefer 2 stories and a bit more space between the house and the boundaries.

I'm currently putting thoughts together for a future (hopefully soon) self build. I often see figures like £2000 per square metre as a guide. I assume that's for a 2 story house. How does it vary for a single story house of otherwise the same construction. So a 200m2 2 story house has a foot print of 100m2 and at £2k per m2, the build cost would be £200k. If that were a 200m2 single story house, with a 200m2 footprint built to the same standard, would would be a good cost estimate?

The parents of a friend of mine lives in a house from the 60s where the whole estate was built with warm air heating. There were vents in the floors and walls and ceilings. They really liked it but all their neighbours had the systems replaced in the 80s with gas central heating. Not for any good reason, parents of friends said. Brits have a very rigid way of thinking at times. "There is only one acceptable way to do things". It used to be coal. And then it was gas. You'd be labeled a weirdo for having anything else. 20 years from now most houses will have heat pumps. 20 years after that we'll have a generation of people who have known nothing else. Except for their weird granddad who still burns dinosaur fart.

My garage is like that. I use it as a workshop. If I've been in there a while in cold weather, condensation forms on the roof. I don't know the remedy but I know it's a problem.

How does that work then? With a combi, you're only going to run the hot water for a couple of minutes to fill a sink or 15 minutes in the shower? With a 200l hot water tank, say, an 8kW heat pump would have to be on for an hour and a half to fill it. Or does heating demand trump a hot water timer?