Cost of building attached garage fully DIY?

[loply]

Hi folks,

I'm considering building an attached 'double garage' on the side of a 3 bed semi I own.

I would do all of the work myself from excavation to bricklaying, roofing and electrics (though getting someone to sign off the electrics, obviously).

The plot on the semi is very large and I can run the garage the whole depth of the house (8m), and out to about 4m, giving me roughly 30sqm.

The garage actually won't have cars in it but will be a workshop, though I will fit a garage door for moving big things in and out.

As mentioned we're looking at about 30sqm with about 15m of cavity walls, I won't insulate the walls, and a flat felt roof. It will need both planning permission and building regs as it's too wide to not require PP.


The price seems a bit low to me so I'm wondering what I've missed or whether I've not put enough cost in for some things. Would appreciate any advice.

Grand total - £6,083

Foundations and Slab Floor - £2060
Disposal of existing concrete paths etc 1x skip £150
Digger for excavation works 1x hire £220
Drain modifications Estimate – pipes/juncs £50
Concrete for footings 17m^3 @ £70/m^3 £1,190
Concrete for floor 30sqm @ 0.15m £350
Sand & Hardcore for floor Guess £100


Cavity Walls - £1269
Wall starter kits x4 £45
Bricks 8+3+4 = 35sqm of walls £625
Breeze Blocks “ “ £239
Mortar Total guess £50
Wall ties x80 £30
Lintels 2x 2.7m + 2x 90cm £280


Roof - £846
Roof joists every 60cm = 12 £216
Roof ply Roughly 12 required £300
Roof felt + underlay 30sqm @ £6/sqm £180
Led flashing 7m worth £100
Tar boiler rental £50


Internals - £1258
Floor paint £30
Wall paint £60
Plasterboards 16 ea @ £8 £128
Plastering £220
Electrical wiring + sockets 15 sockets (3m each) £90
Lights 9 off £270
Laminate floor 15sqm (half of garage) £80
Doors (self made) Steel frames + ply line £150
Windows 2x 90cm windows £230

Misc Extras - £650
Council fees Guess £250
Sundries (nails, screws, etc) Guess £250
Tools I don't already have Not many £150


Cheers,
Rich

 

[bignigeo]

I can only comment on your brickwork side being a bricklayer and I think you are a bit out bricks 2100 the price will depend on the type they will have to match the house, if it is a old house could be expensive
blocks we use 7n concrete and best price we can get is 80p each so allowing for cuts ect for 35m2 you need 38.5m2 £308 mortar I would say looking at around £150 including febmix wall ties you will need around 130 as up the door and window reveals you need a tie every 225mm
you will also need dpc for ground and up the doors and windows unless using thermobate but as you are not insulating thermobate seems pointless lintols also seem cheap have you allowed for a 150mm bearing on both sides of the openings also depending on which way your joists will run garage door lintol may need to be heavy duty.
hope this helps

 

[bignigeo]

just re read your post you haven't allowed for blockwork in the footings and DPM for the floor

 

[loply]

Cheers mate, I've adjusted my costs for the brickwork, not sure how I got it wrong! Also added in a DPM.

Lintels on Wickes only £109 for a 2700mm steel one, plus a couple of small ones for some 600mm windows, joists will run from the outside wall to the attached house wall so the garage door lintels (one at front and one at back) are not really carrying anything - just a soldier row of bricks and it's share of the roof weight!

 

[kingandy2nd]

what's your skill level like?

have you laid bricks before or built a flat roof?

just thinking you may need to allow for wastage.

you could consider just tape and filling the plasterboard rather than plastering if you wanted to save there.

also if it were me i would insulate the walls/ceiling to allow the space to be utalised for other purposes in the future.

 

[pred]

My bit of advice is to get the flat roof done professionally with fibreglass, the life span on felt is 10yrs, they make boats out of fibreglass.


http://www.cybglassfibre.co.uk/general.asp

 

[loply]

I've done a load of DIY and general small construction over the years but this will be my biggest project. I'm confident I can do the research and take the time necessary to get it right.

I can't decide at the moment whether to submit just a building notice or to draw up full plans?

My only concern regarding regs is about the span of the flat roof.

The garage actually tapers - it's 3m wide at the front of the house, and 5m at the rear, which leaves a 1m walkway down the side of the garage before you hit the garden fence.

The flat roof joists therefore need to be spec'ed for a 5m span. I don't know what the BCO will want in terms of whether I need to carry the 5m spec right down the garage (even when the span becomes only 3m!) or whether I can lighten the timbers as it proceeds. Also don't know for sure what they'll insist on in terms of piers on the long brick run and whether they'll want steel in the roof somewhere?

I have worked on the assumption I will be tapping into an existing main drain (which will be inside the completed garage, so will need a new covering?), running an underground pipe to a convenient spot near the outside corner of the new garage, and putting a gully in to catch rainwater from a gutter with a downpipe.

Cheers,
Rich

 

[pred]

I've done a load of DIY and general small construction over the years but this will be my biggest project. I'm confident I can do the research and take the time necessary to get it right.

Know your limitations, I was toying with the idea of buying all the necessary bits and pieces to do the fibreglass roof myself, I got a quote and it was cheaper than what I could buy all the stuff for, he buys in bulk and has his contacts.

 

[noseall]

Treble the price and you may be somewhere near.

 

[loply]

Treble the price and you may be somewhere near.

Thanks for the unhelpful and undoubtedly inaccurate response.

 

[^woody^]

Treble the price and you may be somewhere near.

Thanks for the unhelpful and undoubtedly inaccurate response.

Yes noseall

Please sit down for a few hours and work this out properly for the OP. And make sure its fully itemised too

 

[noseall]

Thanks for the unhelpful and undoubtedly inaccurate response.

Why unhelpful?

Because it is a sniff of reality or that it demonstrates the financial naivety of a typical amateur?
You go build yourself a 30m² garage for £6k then fork out another £3k to get it demolished.

 

[loply]

I have stood inside a couple of garages more complicated than the one I proposed and of similar size which were built for under £10k, so I'm not sure how you reckon mine would cost £18k for 3 walls and a flat roof.

I posted what is a relatively exhaustive list of the component parts of the garage and pointed out that I'd be doing all the work myself, and asked if anybody could spot any items I'd missed.

You chimed up with a meaningless post which was both factually wrong and accomplished nothing. If you can see something I haven't budgeted for which adds to my cost please let me know. If it adds £12k I'll accept your comment and apologise.

The first poster was very helpful and made a contribution, this is a forum, for discussion and contribution.

 

[loply]

noseall, just to try to bring this back to a discussion rather than an argument I've found a couple of examples online to show you, perhaps you could let me know where the misunderstanding is.

This guy said he paid under £6k all-in for his detatched double garage, he got the facing bricks for free but he's had to buy roof trusses and nice looking roof tiles: http://bbs.scoobynet.com/diy-39/568283-my-diy-garage-build.html

If you have a look on this thread http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=3989&highlight=brick there's a post by ukdave2002 showing his 4 car garage which is substantially larger than mine (with a mesanine floor practically!) and again he stated his material cost was about £6k in a separate thread, although I think he called in labourers in the end.

Also see the post here http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=6286&start=0 by brianm, he got a 3-car garage with a loft built for him for £23k all in, doesn't say what the material cost is but that cost was evidently for an 8 week build which he managed but used builders.

Scroll a few posts down in that thread and there's a guy with a timber double garage which he states was under £5k, not that mine would be timber.

I'm genuinely interested why you think a 30sqm garage with three walls and homebuilt doors would be £18k in materials? Have I missed something drastic, or have you misunderstood what I'm building?

Cheers,
Rich

 

[noseall]

There are several ways to acquire materials for building all of which differ immensely.

I work in a world where people want a building like yours constructed and finished in a few weeks therefore i pay a premium for products that need to be acquired and assembled swiftly.

I base any pricing given on that criteria.

However, diy'ers are free to take ten or twenty years to build the same garage whilst in effect sourcing the mat's for nowt or chance it on flea-bay if they wish. You asked for a pro's version and you got it, whether you like it or not.

Good luck in your project and i admire your frugal tenacity.

P.S. If it is any consolation i think your base-work price is the least accurate, i.e. the greatest under-estimation.