Loft conversion questions

I totally appreciate that this is how long is a piece of string stuff and that the devil is in the detail. However, having asked and read similar questions to this I think it’s really helpful to hear other people’s thoughts so…

We’re looking at a loft conversion. There’s nothing obvious to suggest it’s not going to be a relatively simple job. No steels or other fancy stuff. All internal walls are load bearing. We’re also not looking at high standard finishes. The big structural things are a staircase and windows. The windows are 3x velux and a gable window that will replace an existing one. The total area is c30m square. It will be a bedroom and a shower room.

What are your thoughts on costs for this? One builder told us 2k per square meter.

The more specific question is costs for insulation. They will need to insulate between the floor and ceiling of lower floor and also between roof and ceiling of conversion. One quote has the cost of this as £21k which seems outlandish. Any thoughts on that?

All input gratefully received. 🙂

£21k seems very cheap for a proper loft conversion with all the regs accounted for to me.

£21k seems very cheap for a proper loft conversion with all the regs accounted for to me

The £21k was just for the insulation (and I assume cost of fitting).

Why do you think you won’t need steels?

Caroenter and run my own building firm of 25 years, all lofts will require some sort of steelwork to work officially.

Are you just wanting to do a cheap hash of a job and “convert” your existing dusty loft to a bedroom or do you want to do a proper job that will he signed off with building control and be an official habitable room.

Your existing ceiling  joists that form the floor of your existing loft are NOT floor joists, as a minimum you will require larger floor joist, probably 8 inches or 200mm deep,  to take the additional loading of a bedroom and bathroom, you don’t want the extra weight being transferred down into your 1st floor ceiling, hence needing steels to provide you with a new floor separate from the existing 1st floor ceiling.

Or, you could strip out all 1st floor ceiling joists that are most likely to be 4inchs deep and replace for 8inch joists, you’d possibly be able to reduce the amount of steelwork needed that way.

Either way it’s not cheap, a proper loft nowadays in my area, N London/Hertfordshire will costs £60k minimum

Why do you think you won’t need steels?

Caroenter and run my own building firm of 25 years, all lofts will require some sort of steelwork to work officially.

Are you just wanting to do a cheap hash of a job and “convert” your existing dusty loft to a bedroom or do you want to do a proper job that will he signed off with building control and be an official habitable room.

We have a structural engineers report following architects drawings which indicates that steels are not necessary. We’ve been told that some doubling up of existing beams will be sufficient. The house is a bit of a 60s oddity and seems to be over engineered in a variety of ways!

Obviously we’re looking for everything to be legal and above board.

probably 8 inches or 200mm deep

Existing joists are 7″ and all the internal walls which they sit upon are brick so the spans are not huge.

From.memory 7inch beams are about a 3.5m max span with c16 a bit more for c24. Whats the truss? You gonna cut out anything? 3.5m isn’t very much.

You need a structural engineer to get building control to sign that off.

Not your own opinion, and not a builder an actual qualified structural engineer. Because that price could jump.

Well that is unusual indeed, to have ceiling joists as large as that.

If you’ve had an architect and structural engineer look at the layout then it sounds like it is doable then.

Insulation is expensive and now we have updated building regs to meet the price would be more expensive again, I’m not shocked by the price, seems possibly abit high for just insulation only, but I would imagine there’s more work involved than meets the eyes.

Who is doing the rest of the work needed?

You need a structural engineer to get building control to sign that off.

As I said above, we have a structural engineers report.

I’m not shocked by the price, seems possibly abit high for just insulation only, but I would imagine there’s more work involved than meets the eyes.

Thanks for that, it struck us as crazy but maybe it’s not. There’s some stuff that punters can have an idea of the price of and other stuff maybe not.

Who is doing the rest of the work needed?

We’ve only got one quote so far. It’s a young company that seems to be a joiner and a project manager. They have plumbers and electricians they work with. Plumbing and electrics quotes seem reasonable.

The £21k was just for the insulation (and I assume cost of fitting).

just the insulation in the roof?

if its just kingspan cut & stuffed between the joists then yes that’s a lot, even if theyre plasterboarding and plastering as well it seems pricey

I would suggest you get a second opinion on the structural aspects, from another certified structural engineer

I would suggest you get a second opinion on the structural aspects, from another certified structural engineer

Why so? That’s going to be a significant cost.

The insulation between the joists will just be glass wool for sound insulation, not expensive. There will probably be 75mm Kingspan between the rafters with 62mm Kingspan backed plasterboard overlayed. Maybe five to eight grand in materials there. Could be 300 man hours to fit all that. Joists will need doubled around the stairs opening and rafters doubled next to Veluxes. Depending on the type of membrane under the slates or tiles you’ll maybe need roof vents.

Sixty thousand is probably about right, it won’t be less (in Edinburgh some trades are charging £100 and hour, supply and demand is the driver!).

Why so? That’s going to be a significant cost.

the reported over engineering sounds odd, why would a builder do that ? Extra cost for no gain…. I’d want to be doubly sure it is the case.

Rather than ‘sweat’ the cost of individual parts of the conversion I’d be looking to get a couple of ‘fully delivered’ price quotations, it could be that the total price is just too much for what you’ll actually gain (could be as others have pointed out, well past £50k inc VAT for a bedroom & ensuite).

A few years ago we renovated one of our barns as a home for my Mum, got 3 quotes, the price range was huge; cheapest was 2/5th’s the price of the most expensive, we went with the middle price (plus I’d used the company at work for a complex job and knew they employed people who could ‘do’).  And agreed ground rules; focus on price & quality, time not so big a deal.  More than happy with the results.

Doesn’t sound like you’ve had formal quotes yet if you are getting m2 quotes?

If you’ve had one for 60k fully signed off, including the bathroom I’d say that is a really good deal.  People are quoting 15k just to fit and tile a bathroom round my way.  11k quote for painting a hallway (inc. woodwork) etc…. so I’ve been doing it myself….

Interested in the topic as at some point in the next 5 years we may well look to a loft conversion too.  My plan is to get a builder in for the structural stuff and then do the rest myself.  I ended up dealing with building control myself on our kitchen extension and they were actually really good and helpful

So we’re doing a very similar thing, having our loft converted but we’re going for a dormer and hip to gable conversion on a 3-bed semi, its going to be a master bedroom and en-suite.  For the full job we were quoted anywhere between £66k and £140k in Norwich, the top one clearly didnt want the job and that’s fine.

My other half decided to test my DIY skills and offer up a compromise of someone doing a structural only build and I finish everything off inside. Again, quotes came back from £36k to £55k which seemed more reasonable.  The company we went with were the only one to give us a load of examples of their previous loft conversion and have been in the business for around 35 years and came with tons of recommendations from people we knew and yes they also were the cheapest but also the most qualified and do this day in day out.

Anyway beside all that, you don’t need steel for it to be officially signed off, it just needs to meet building regs and they don’t say anything about requiring steel. Our structural engineer also agrees that steel is heavy and massively increases labour costs.  Yeah its strong but not needed at all if its built properly and meets structural requirements.

Your insulations costs are mental, sounds like they’ve just pulled a number out of their ass and added it on, its probably mostly labour costs and fitting PIR boards properly is a pain in the arse, add on gapotape and yeah the price shoots through the roof, literally. Its like £100 a box, contains 5 rolls each and then they are only 10m in length and you’ll need a ton of them.

Anyway starting to ramble now.  The company we picked is doing everything structural – so stairs, fitting new floor joists, fitting the windows and building the dormer and making sure its all waterproof obviously. Structural work only is £36k I’ll be handling everything else with the FIL doing electrics and a mate sorting out the plumbing if I cant do it…

As I said above, we have a structural engineers report.

you’ve got a report which I’m guessing says “yes this is feasible, double up the floor and internal walls are load bearing”.

what you need is a set of calculations (and at the minimum, a sketch drawing showing what those calcs describe) that reflect what you are actually planning on building, including what is going to happen around the new hole you are making for the stairs, and proving the roof timbers work in the new arrangement (and with added weight of insulation etc, some 1960s roofs didnt ‘work’ in the first place).

one thing that sometimes catches people out, as you have a second storey, it must have a route of escape from that room to outside, that is fully separate from the kitchen – i.e. if you’ve got an open plan downstairs that the stairs come down in to, you’ll need to do some rearranging.

11k quote for painting a hallway

Seriously? How big is the hallway and what are you painting it with?

in Edinburgh some trades are charging £100 an hour

I’ll never forgive my parents for forcing me down the office route line of work as tradesmen were poor plebs according to them

4 internal doors, one external with 1930s orignial windows either side, 2 further windows, staircase and understairs cupboard, skirting and architrave.  11k.  and I was supplying the materials (edit well, the paint)

Its taken me about a week, on and off.  not including the doors themselves.

It takes me a lot longer than a week to earn 11k.

Apologies Spin. I did read your posts but missed that detail because you hid it behind architects ?

Painting rooms is one of my least favourite DIY jobs, but at those rates I might consider a career change.

It takes me a lot longer than a week to earn 11k.

It is insane what some trades are now charging – but they are busy, so they try it on (amount it will cost is probably based on how flash the cars that are sat on your drive are). If they don’t get it, they don’t care because the next day someone else will be asking for the same thing. When they don’t have a long waiting list of customers, their prices will come down.

That insulation cost does seem insane, without penny pinching too much id call around a couple of builders merchants to get an idea of the cost of goods, add a reasonable day rate plus a % for extras so you’ve got a rough idea to begin with.

I insulated a small annex in the summer only 3.5 x 2.5 with a pitched roof, the walls are non insulated so I went a bit mad with the roof insulation and specd 200mm PIR total, 150 between with thinkened rafters, 50mm underneath, VCL then Plaster boarded. Gave Building control the U value he wanted plus spare.

There are a few places that sell good seconds PIR board, I got mine from one and it was as new not even a small dent in any. From memory the 150mm 1.2×2.4m was about £50 each, 50mm was £30 maybe. The lot came in well under £500. Cutting and fitting is a total pain but not rocket science to get a tight fit.

Structural eng was around £150, I’d vaulted the ceiling so had him in to spec center beams etc and keep B/C happy. Had two Velux fitted £250 per window, he needed 3×2 timber for the framing which was around £40 from the yard (I’d pay more to have the windows done next time as he left a couple of marks but not as big as the one I made on the handle with the bloody ladder) vent tiles are £30 for my type, you’d probs need 4 all in – whole lot materials wise inc Velux + fit was under 3k?? Much much smaller I know.

It’s all relative but 60k is a lot to me, my house was £115.. but I’d be speaking to a few builders/roofers etc, if you know a good sparky and plumber get them in and PM it yourself and see what each end of the cost/b’ache scale looks like.

As above B/C are really good and I’ve used mine loads just to pop in when passing to discuss if I’m doing stuff to spec

I can’t believe there’s people quoting £11k for painting a hallway! I’d want my house done twice for that! I did get quoted 3k to fit a.2m RSJ though, the guy that did it did it for £500 and I still slightly begrudge that as everything was exposed and the job took 5hrs all in and he left me all the waste!

I had my loft fully insulated, boarded, roof aired and 2 lights installed for less than 3k 2 years ago.
Post Covid so maybe needed the work. Used for storage only not living space

had my loft fully insulated, boarded, roof aired and 2 lights installed for less than 3k 2 years ago.

Things are easy and cheap when you don’t have to adhere to structural, efficiency or living space safety standards.

Having been involved in a new build where the heat pump we installed wasn’t working as the house didn’t reach temperature I would be very careful project managing anything unless you have experience. Also unfortunately insulation is often installed by labourers and they have no concept of why it needs to be done well or the implications of not carrying it out properly.
We reviewed all our calculations for the heat pump and it will as sized correctly, what we didn’t allow for was the plumber employed by the client downsizing the pipework we specified to supply the underfloor or the fact that entire gable walls are completely uninsulated, windows which appear to be leeching heat around frames along with many other areas of concern including air tightness.
What should have been a dream home will need a lot of remedial work to get it to standard.

Also unfortunately insulation is often installed by labourers and they have no concept of why it needs to be done well or the implications of not carrying it out properly.

This applies to pretty much everything that has been done to my house for about 100 years.

For the latest round of bodging that did include some loft conversion the insulation is that foil multilayer blanket type stuff. Attached directly to the rafters. I removed some in an uninhabited space as we had a leak. No idea how air is supposed to circulate behind that if you don’t cross batten the rafters… Odd how lenders are against spray foam but happy for all kinds of crap to be hidden behind plasterboard in a loft conversion.

No idea how air is supposed to circulate behind that if you don’t cross batten the rafters

In mine it circulates between the rafters over the top to the other side

That’s the way it was built in 1952.

That makes sense – never really thought it through it for a normal roof. We don’t have a conventional roof construction so there is no ridge, it terminates against a flat roof.

No

Thanks for the input folks, given us a few things to think about.