Breakdown of 2 story house extension

okhajut

We have about 27m of garden behind the house. I think that an extension for room would be a good idea. I am interested in a 2 story extenstion. It will make the house building longer by about 5m and a bit more if a bathroom is attached at the end.

This type of two story extension is going to cost a lot but I think I will only want to make it 4 or 5 years from now depending on how many more kids I am going to have.

Now the reason for this question being posted here is to understand the breakdown of the work that is required to create an extension itself which would start with digging trench and pouring concrete for the foundation I believe and then end with painting the walls once the radiator pipes and wiring is installed I believe. This includes bricklayering and plastering and then putting the roof in place. I am not sure of the full list of what are the different parts of the work.

I want to know, what aspect of extension work is the most expensive? Is it wiring? Is it the roof? Is if the foundation? Is it possible that over the next few years, I can try to find a way to learn atleast one skill e.g bricklayering or plastering, and then use this to reduce the extension cost by doing the work myself?

I would expect that 5m extension behind the house with such vast garden should be possible. But I do not know the law.

Bigphil1474

You need to consider whether you want the extension to come under permitted development (Class A), or whether you'd want it to be the size you want and end up needing planning permission. In simple terms there are limits under PD depending on the plot of land the property sits on, the size of the extension and the square meterage within the extension. Based on what you've said, the plot size won't be an issue, but a two storey 5 metre extension won't be covered under PD, but it could be a PD if it is less than 3m (I think from memory). You could tweak your plans to make it fit - easier than having to go through for planning permission. PP is not expensive but can stop plans in their tracks. Will also depend where you are.

You will need to have some architectural drawings for PP, and you'll need them anyway to make sure the extension is built properly. Probably not the most expensive element. The building will also need Building Control sign off. 

The foundations and building of the extension will probably be the biggest cost, and much of that will be labour costs. A two storey extension will need scaffolding as well. I don't think the building of the extension is something you should try DIY to be honest. Costs can vary but a ball park of £2-3k per square metre won't be far off depending where you are.

The finish costs could be significant depending what you want in the extension e.g. new kitchen. You'd normally expect the builder to build your shell - Essentially a plaster finished interior with roof, windows, wiring etc. in place - make sure this is considered in the plans. You can't DIY electrics. You could opt to DIY the plastering but personally I'd suggest it's a bad idea - doing a bit of repair plastering as a DIYer is fine, but fresh plaster on a new build is probably a disaster in the making. I suppose if you spend a few years training then possibly.

Decor is the most obvious way you can DIY and save some money. Painting, wallpapering, fitting skirts etc. are all relatively simple jobs you can learn. Even fitting a kitchen isn't beyond a competent DIYer (minus the gas and electrics).

I'd recommend seeing if you can get recommendations for a good builder, invite them round to discuss your plans and rough estimates. Bear in mind any estimates you get now will be way lower than what you'd pay in 5 years. Alternatively, have a look round where you live, see if anyone else has had an extension like the one you are thinking of, have a chat with them and see what they say.

Section62

okhajut said:

I want to know, what aspect of extension work is the most expensive? Is it wiring? Is it the roof? Is if the foundation? Is it possible that over the next few years, I can try to find a way to learn atleast one skill e.g bricklayering or plastering, and then use this to reduce the extension cost by doing the work myself?

If you employ one builder/contractor to do all the other work for you then there's a good chance what they charge will be increased by as much as you may save by DIYing part of it to account for the 'hassle' factor of fitting what they need to do around what you've chosen to do yourself.

In effect most general builders also act as project managers - making sure the right trades turn up on site at the right times, and that work is done in the correct sequence.  If you are living in the house while the work is being done that will potentially make the job more complex, but wanting to do some of the work yourself would take things to a different level of 'complicated' (Read: expensive)

The alternate way to do it would be for you to act as project manager and hire in the trades as you need them.  But starting with zero experience, the chances of you saving money through this route are zero or worse.  Self-project managing is more suited to people who have at least some prior experience and are tackling a money-not-the-object lifetime home project where doing things the way they want is more important than saving a few thousand pounds.

Section62

Bigphil1474 said:

You need to consider whether you want the extension to come under permitted development (Class A), or whether you'd want it to be the size you want and end up needing planning permission. In simple terms there are limits under PD depending on the plot of land the property sits on, the size of the extension and the square meterage within the extension. Based on what you've said, the plot size won't be an issue, but a two storey 5 metre extension won't be covered under PD, but it could be a PD if it is less than 3m (I think from memory). You could tweak your plans to make it fit - easier than having to go through for planning permission. PP is not expensive but can stop plans in their tracks. Will also depend where you are.

You will need to have some architectural drawings for PP, and you'll need them anyway to make sure the extension is built properly. Probably not the most expensive element. The building will also need Building Control sign off. 

On the whole it isn't a good idea to make an extension smaller to fit within PD rules if you started out wanting something much larger - adding an extra metre or two to the size of a rear extension typically gives much more value than cost, so negates any increase in cost involved in applying for planning consent.

If plans are needed for Building Control (and in any case having some kind of plans for a project is sensible) then the principal consideration for getting planning consent is allowing enough time to get it (not an issue for the OP with a 4 or 5 year timeframe).

If consent is refused then the plans could be amended to meet the planner's concerns - or if PD existed in the first place then simply revert to building up to the maximum allowed by PD.

On the whole, not applying for planning consent for an extension (and going with PD instead) is only really worthwhile if either a small extension is what is wanted, or else if there is some kind of deadline and the project manager hasn't allowed enough time to get consent.  And if the latter then the first thing to do is to question the sense of the whole project rather than plough on, because otherwise there may be bigger problems ahead.

victor2

You will need proper drawn up plans done by an architect for planning permission, which you will almost certainly need for a two storey extension. There'sa no reason why you can't get them done a few years ahead of the project though. Planning permission usually has a date (like 3 years away) by which the work must have started, but no finish date.

I know someone who just bought a house with such planning permission granted over 10 years ago and a start requirement of 3 years. The foundations are done but nothing else.

A good architect will highlight such issues as building over shared sewer pipes or problems with nearby trees etc. For example, we had an extension built over a shared sewer, which the water company are responsible for. We had to get a camera inspection done before the work could start, to make sure there was no damage or work required to it, and afterwards the same inspection done to make sure the work had not caused any damage. The foundations had to go down below the sewer pipe, which had to be boxed round to prevent the concrete having any contact with the pipe. That involved extra work and cost, before even a single brick was laid!

If you've watched bricklayers and (particularly) plasterers at work, you soon realise it's not a skill you can learn overnight - it takes years of experience to get a quality finish. Fitting skirting boards and decorating are probably the most you'll want to do yourself. I did fit the light fixtures - after I had determined with the builder where the light fttings would physically be so that the wiring and switches would be in place.

grumbler

victor2 said:

You will need proper drawn up plans done by an architect for planning permission

Some time ago my friend got a permission with DIY plans.  It was a two-storey side extension. Not sure that he even used Google Sketchup or something similar. Yes, structural calculations, if needed, will possibly require a professional.

ETA: My other friend paid £2K+ to an architect who failed to address such an obvious problem as the minimum tiled roof pitch for a 4 meters deep lean-to 1-storey part of the extension. As a result, the old windows on the first floor had to be lifted up and replaced (I know, other solutions are possible). Hardly a surprise that after getting the money the architect disappeared and stopped answering even phone calls, let alone e-mails. And it wasn't a random architect. He was recommended by some friend.

tacpot12

I'd recommend having a look at the Gosforth Handyman channel on YouTube. Andy McCellan who runs the channel has recently completed a two story extension to his house. As well as documenting much of the process, he has three videos where he discusses the cost and timescale for the project, and also how to find a good builder to do the work. In that video last he explains how the general builder will also act as a project manager, ensuring materials and other trades are on site when they need to be. The project manager role is massive and will stretch anyone who isn't to organising the work of others as part of their normal working life.

stuart45

Drawings for Planning permission are much more basic than those required for Building regs. I did my own for my extension, and used a Building notice, so didn't need a more complex drawing for the regs. 

Swasterix

As somebody who is 2/3 or the way through a double storey extension, I can tell you with some certainty that it ain’t going to be cheap. 

In the North Easy (cheap, yeah right). We’ve built a 9m x 2.5m double storey, with a 5m x 4m single storey on the back. Builder built the shell, I’ve paid an electrician and I’ve committed to doing most of the rest myself. I’ll likely have no change from £100k….

Will be mint when it’s finished though, or so people keep telling me 😁

Swasterix

grumbler said:

victor2 said:

You will need proper drawn up plans done by an architect for planning permission

Some time ago my friend got a permission with DIY plans.  It was a two-storey side extension. Not sure that he even used Google Sketchup or something similar. Yes, structural calculations, if needed, will possibly require a professional.

ETA: My other friend paid £2K+ to an architect who failed to address such an obvious problem as the minimum tiled roof pitch for a 4 meters deep lean-to 1-storey part of the extension. As a result, the old windows on the first floor had to be lifted up and replaced (I know, other solutions are possible). Hardly a surprise that after getting the money the architect disappeared and stopped answering even phone calls, let alone e-mails. And it wasn't a random architect. He was recommended by some friend.

I had a similar experience to your friend… I did the drawings for my “Architect” and gave him a simple brief which was that I wanted him to tell me whether what I had drawn was possible in reality. I was very, very specific in what I wanted and what I had envisaged, how things would be laid out, etc… all cool he said. 

There have been a number of things that he has completely missed including a similar issue with the pitch on a 4.5m lean to roof (its now flat), a steel that would have crossed in in front of a stair at around 300mm high. When all is said and done I’ll be asking for my money back. It’s a good job that I was lucky enough to find a very good and creative builder!