2 phase extension / remodel cost expectations

[GasManDan]

Good afternoon all, 

Newbie here - I stumbled across the website last night and have been looking on it since-lol

 

I live in a 1950’s 3 bed detached house and have had an architect and structural engineer draw up plans for a 2 phase extension; the first being a rear single storey pitched roof with vaulted ceiling + bifold doors, and the second being upstairs above garage and double bay oak/oak clad (?) front bay. 

The plan is to start at downstairs internals then work our way up - phase 1 (downstairs) is the above mentioned rear (consisting of goal post style steels & 2 internal steels (8 in total)....n.b already have 2 steels in place in the house as it is as is already a flat roof extension!) the measurements of the new pitched roof extension is just over 12mtrs across & 5 mtrs out. 
 

I have had 5 quotes now for building the shell of the extension (up to sub floor & water tight-no internals) fitting 2 internal steels & building 1 internal wall.....not sure if I am being a bit delusional here but I was budgeting roughly 30k for this work but the quotes I’ve had back range from 52k up to 86k!! 
 

Does the 30k sound like I was being a bit apprehensive??  Because the quotes vary so much I now have no idea as to what is a sensible  quote! 
 

Just to confirm; the biggest steel in phase 1 is 203x102x19kg
 

Thabks in advance for your help and feedback

 

 

[Russell griffiths]

How much can you do yourself ??

you could get separate teams to do bits. 

Get the footings in then get a bricky, then a chippy then a roofer. 

[DevilDamo]

Where are you/the property located?

 

Down here in the south, I’d be using a rate of £2k per sq.m so your rear extension alone would be coming in at £120k!!! Even a rate of £1k per sq.m is around £60k. Where did your budget figure of £30k come from?

[GasManDan]

3 hours ago, Russell griffiths said:

How much can you do yourself ??

you could get separate teams to do bits. 

Get the footings in then get a bricky, then a chippy then a roofer. 

All internals (plastering, flooring, tiling, electrics, gas etc) I plan to do myself-only thing I can’t do good is lay bricks. I don’t mind putting footings in but am a bit unsure about when/how to put the goal post steels in!? 
 

3 hours ago, DevilDamo said:

Where are you/the property located?

 

Down here in the south, I’d be using a rate of £2k per sq.m so your rear extension alone would be coming in at £120k!!! Even a rate of £1k per sq.m is around £60k. Where did your budget figure of £30k come from?

I live in the West Midlands. 
The budget of £30k is what I roughly guesstimated based on material costs etc. 
 

I appreciate there is some work involved in the steels etc but am more than willing to get stuck in and dig footings etc 

[DevilDamo]

If you were a general and all round builder, I could probably understand why a figure of £30k would be considered reasonable. To me, even for a general builder, it still is very cheap.

 

Do your ground conditions permit traditional strip/trench fill foundations or would they be at a depth for piles to be considered? Is the new ground floor to be a solid ground bearing slab or is a suspended concrete/timber floor required, again due to the ground conditions? What door and window including rooflight configurations do you have?

 

With a 5m span (front to back), you’d probably be looking at a 225mm deep B&B floor, assuming you were gong down that route. Or the other option is to span the floor side to side with sleeper walls and spans of 4m. Your rafters may also be in the region of 225mm deep and could potentially require some flitch or steel beams if you were going for a hipped roof as opposed to a lean-to. You just have quite high first floor window cills in order to accommodate the minimum roof pitch, flashings and rooflights?

[GasManDan]

11 hours ago, DevilDamo said:

If you were a general and all round builder, I could probably understand why a figure of £30k would be considered reasonable. To me, even for a general builder, it still is very cheap.

 

Do your ground conditions permit traditional strip/trench fill foundations or would they be at a depth for piles to be considered? Is the new ground floor to be a solid ground bearing slab or is a suspended concrete/timber floor required, again due to the ground conditions? What door and window including rooflight configurations do you have?

 

With a 5m span (front to back), you’d probably be looking at a 225mm deep B&B floor, assuming you were gong down that route. Or the other option is to span the floor side to side with sleeper walls and spans of 4m. Your rafters may also be in the region of 225mm deep and could potentially require some flitch or steel beams if you were going for a hipped roof as opposed to a lean-to. You just have quite high first floor window cills in order to accommodate the minimum roof pitch, flashings and rooflights?

Thanks for the reply mate. 

 

The honest answer is I’m not sure regarding ground conditions; next door have recently done a flat roof rear extension and they used the traditional strip/trench fill foundations. It will be a solid concrete slab as is the current extension with the air bricks being sleeved through to the original suspended timber floor 

reference to door and window config; we are planning to have an 7 leaf bifold and 3 velux roof lights.....3 of the quotes we had didn’t include these! 
 

originally our architect spec’d a 15deg roof tile but we requested that it was changed to the min 12.5deg in order for us to be able to take it out a little further.

[DevilDamo]

Was your current extension built with BR’s or was it exempt? If the latter, the ground floor construction could have been whatever you like. As this new extension will be notifiable, your ground conditions would really dictate your ground floor construction. Building Control should be able to shed some light on this as they’ll know the conditions for the area. Or you could speak to your engineer. Failing that, good old fashioned trial holes would confirm your options.

 

How wide are your bi-folds for them to have 7 panels?

 

If you’re opting for 12.5 degree roof, you may well need Velux’s flashing kits in order to take the angle of their rooflights up to 15 degrees. Don’t let your builder try and make these on site. Check your tiles can also go down that low too. I’d never look to specify anything less than 15 degrees as it just reduces your tile/rooflight options.

[GasManDan]

I’m not sure re the current extension as we have only lived there a few years and think the extension was built around 15yrs ago. We went through planning as changing the front & upstairs in phase 2.

 

the bifolds will be almost 6.5mtrs.....I’ve attached a pic of the proposed new floor plan. 
 

as mentioned previously, the architect did plan for 15deg roof but when I chalked it out, felt we wasn’t gaining that much more to what we have now. I think the velux on the vaulted roof section should be ok hopefully but might need to do something with the one spanning out from the house. 
 

we currently have dreadnaught clay tiles on the house and ideally would like something similar if not the same but obviously I need to check they can cope with the 12.5 deg pitch