Basement thoughts

[Pocster]

1 minute ago, pocster said:

Just find a man with a big digger ?

[puntloos]

7 hours ago, pocster said:

IMG_5973.MOV

 

[puntloos]

Thanks @Bitpipe - a ton of useful detail! My key question about all this is 'when to start this process'?

 

We're basically ready to submit for planning permission, should we get the SE out 'now' before we do PP?  Or would you do this legwork while the approvers do their thing?

 

I have no idea how to 'find' a groundworker though. I have one building site right across from myself right now (!) so like you suggested I might just ask them. They're a big construction company but still private (building some appt complex). 

 

11 hours ago, Bitpipe said:

Expect prices to increase /sqm if the basement is small

It is, 3x4 maybe

11 hours ago, Bitpipe said:

, access is difficult

Not sure how to determine this, but assuming the current house is gone there is a 15m wide side to the plot that faces the road, incl a 3m pavement.

 

11 hours ago, Bitpipe said:

 neighbouring properties are close

Again 'close' is subjective.. but the house is planned to be 13m wide on that 15m, so 1m on each side, then the border (a thin fence) and then about 1m on the neighbour's sides as well. Is that close?

 

11 hours ago, Bitpipe said:

and you have challenging ground conditions such as weak ground, high water table or radon gas etc.

 

"I don't think so" - it's standard british clay, but clearly we need to verify this.

 

11 hours ago, Bitpipe said:

When you have the finished basement shell with house on top, you fit it out with the rest of the house.

I found very little of the 'domestic' building services (builders, architects etc) confident to deal with basements. However once I tapped into local GWs then I had lots of options.

Tip - if there are any large public works going on near you, see who the GW contractor is. 

 

But before you do ANYTHING - get a decent ground survey designed by a SE as that will drive all costs as you move forward. Maybe you spend the money and decide you can't afford to proceed but that's better than starting the job and finding nasty surprises that mean you can't afford to finish it.

 

 

Will do.. but as asked earlier: should we try to do this before PP submission or can I take a little time? Of course PP would need to specify the basement but I was thinking to just have a basement completely central in the house (so it would in fact be 7m away from any neighbour! 

 

Basically:

Neighbour - 1m gap - border - 1m gap - wall - 5m away from wall - 3m basement - 5m away from wall - wall -  1m gap - border - 1m gap

 

 

[puntloos]

Has anyone ever considered pre-made basement solutions - eg.

 

http://www.readymadebasements.co.uk/brochure.pdf ?

 

Their quotes are here: http://www.thermonex.co.uk/?q=node/48

 

"16,000 for a 5x5".. I assume that's not including a bunch of hard work (esp the digging, removal)...

Edited June 2, 2020 by puntloos

[Bitpipe]

14 hours ago, puntloos said:

Thanks @Bitpipe - a ton of useful detail! My key question about all this is 'when to start this process'?

 

Get planning first, drawing a basement sized box on your plans will not cost anything. However, you will need to specify any basement elements that connect with the outside street scene such as light wells, exits etc.

 

You should understand from your architect how the basement will meet regs on fire etc - if you do not have an independent exit to street from the basement then you'll need to budget for suppression (i.e. sprinklers) and also plan ventilation in there.

 

Also be clear what it it being used for - or more importantly what it's not being used for (bedroom). Storage is usually a good label  

 

14 hours ago, puntloos said:

We're basically ready to submit for planning permission, should we get the SE out 'now' before we do PP?  Or would you do this legwork while the approvers do their thing?

 

I commissioned our SE work after planning but we had a gap while we waited for our old house to sell so it's really up to you.

 

14 hours ago, puntloos said:

I have no idea how to 'find' a groundworker though. I have one building site right across from myself right now (!) so like you suggested I might just ask them. They're a big construction company but still private (building some appt complex). 

 

Google, Yellow pages, etc. Groundworkers vary from one man and a machine to large operations and many will take on smaller jobs just to keep plant and staff utilised while the rest are off on bigger jobs. If you're going to be self building a house you'll need to practice this still at finding trades and getting them to want to take your work ?

 

They will take you more seriously when you have drawings and specs they can price off but no harm in understanding basic availability and rough cost (with a million assumptions).

 

 

14 hours ago, puntloos said:

It is, 3x4 maybe

Not sure how to determine this, but assuming the current house is gone there is a 15m wide side to the plot that faces the road, incl a 3m pavement.

 

Sounds decent enough.

 

Why is your basement so small if your house footprint is so large? That is quite a compact space and you're going to pay a significant premium for it. An equivalent 'garden room' would be a fraction of the cost and not require PP.

 

What is the plan for the rest of the floor and foundation structure? You don't want an isolated box floating around in the ground under your house and not have it tied to anything else structurally. This is why basements usually occupy a significant portion of the house footprint. Also economies of scale.

 

14 hours ago, puntloos said:

Again 'close' is subjective.. but the house is planned to be 13m wide on that 15m, so 1m on each side, then the border (a thin fence) and then about 1m on the neighbour's sides as well. Is that close?

 

Get your plasn out and work out the party wall calcs - all about intersecting lines at 45 degrees.

 

14 hours ago, puntloos said:

 

"I don't think so" - it's standard british clay, but clearly we need to verify this.

 

SE will help you understand what that means structurally - never to early to start talking to a few, should give you a bit of time for free to understand the project and if you can both work together - you also need to know if they have any experience in this area. Remember they never need to come to site so can be at the other end of the country if needs be.

 

14 hours ago, puntloos said:

 

Will do.. but as asked earlier: should we try to do this before PP submission or can I take a little time? Of course PP would need to specify the basement but I was thinking to just have a basement completely central in the house (so it would in fact be 7m away from any neighbour! 

 

Basically:

Neighbour - 1m gap - border - 1m gap - wall - 5m away from wall - 3m basement - 5m away from wall - wall -  1m gap - border - 1m gap

 

That's fine but see other comments above on how useful that will be and how it works with the rest of the in ground structure.

[puntloos]

Cutting out everything that's understood, with thanks, @Bitpipe - v. useful stuff. A few small ones left:

 

5 hours ago, Bitpipe said:

Why is your basement so small if your house footprint is so large? That is quite a compact space and you're going to pay a significant premium for it.

Well it's all about actual needs vs cost. Even GBP 1 is wasteful if we don't really need it, and I've been working under the assumption that a basement is rarely something that increases the sale value beyond what I've paid for it. Not to mention that a 250m2 house on a 400m2 plot feels about 'the max' anyway. If I were on the lookout for houses I'd raise an eyebrow if I saw a 350sqm house on that plot.. 

 

No? 

 

Main goal for basement is to 'hide away' noisy or bulky stuff and make the garage usable for actual cars, should the need arise. 3x4 is the minimum. 5x5 seems perfect.

Anything beyond that adds to the stuff we don't really need, so unless the next sqm would be almost near free I don't think we'd do it? Or am I being shortsighted? (of course there's also a budget to think of..)

 

Quote

An equivalent 'garden room' would be a fraction of the cost

 

Not sure what you mean.. clearly an actual room-in-the-garden would eat garden space, and we are VERY tight on that, we'd love a larger garden than we have, this already is a sad compromise... 

Quote

and not require PP.

 

Hm? Not sure why not? Both our actual garden room, a theoretical extension later, or a basement need some PP? 

 

I sense I'm missing your point...

 

Quote

 

What is the plan for the rest of the floor and foundation structure? You don't want an isolated box floating around in the ground under your house and not have it tied to anything else structurally. This is why basements usually occupy a significant portion of the house footprint. Also economies of scale.

Fair. My initial idea was literally copying the basement one level down. 

But I figured that if a basement is harder to build if you're close to the neighbours, why not move it more centrally.. but I can see the point of having walls align etc, so perhaps the best mental model is to have it straight below the hall (also less weight, since it's fully open above?) which is 5.8*3.5? 

 

Some people (maybe you?) suggested to do a full basement somewhere (140-odd sqm!) but I doubt that'd pay off, unless somehow the cost of e.g. the foundation would disappear.. 

 

Quote

Get your plasn out and work out the party wall calcs - all about intersecting lines at 45 degrees.

 

Idon't think I've gotten to this part of house building theory yet ? not sure if this is the time/place but can you be slightly more specific? 

Edited June 3, 2020 by puntloos

[Bitpipe]

1 hour ago, puntloos said:

Cutting out everything that's understood, with thanks, @Bitpipe - v. useful stuff. A few small ones left:

 

Well it's all about actual needs vs cost. Even GBP 1 is wasteful if we don't really need it, and I've been working under the assumption that a basement is rarely something that increases the sale value beyond what I've paid for it. Not to mention that a 250m2 house on a 400m2 plot feels about 'the max' anyway. If I were on the lookout for houses I'd raise an eyebrow if I saw a 350sqm house on that plot.. 

 

No? 

 

I'd expect the value a basement (or any specific element of a development - room in roof, garage, swimming pool etc) delivers to a dwelling is really tied to what function it has, what value a future purchaser places on that function and how it works with the house as a complete design.

 

The overall m2 increase obviously helps but if it costs you a small fortune to build and is a bit of a 'meh' (or worse) to a future purchaser then you won't recoup that investment.

 

On the flip side, if it makes you happy to have a place underground to hide stuff and you can afford it then screw the return on investment and do what you want.

 

Big inherent advantage of a basement is that it can deliver valuable dwelling space on a smaller plot, but only makes a good ROI if the area ceiling values can support that. We have friends who bought a tumbledown cottage in a highly desirable local village but were restricted to maintaining more or less the same footprint and massing. No restrictions (other than cost) on going down and they created an amazing contemporary home and even the significant cost of their basement (underground stream basically flows through their plot to the Thames) the ROI stacked up given relative property values.

 

For many of us on here who have built low energy dwellings, even passive, we're more than aware that our SAP A rating is of little interest (and value) to a potential buyer and may even put them off. Location, street view, aesthetics, nice kitchen, bathrooms and whatever layout is in vogue will ultimately sell the house.

 

I think looking at what dwelling size and property ceiling values your location will support etc is a very sensible way to proceed. Our street has houses that range from £350k bungalows on small plots to £1.5M detached on 1/2 acre. Given our plot is about that size, we could justify a 400mm2 dwelling with six beds & full basement etc as the plot and street value will carry it.

 

Our basement is habitable functional space, occupied the whole footprint and represents about 28% of the whole house floor area ex- currently two teenage dens / tv rooms / music rooms etc plus a gym and a book / craft room (still figuring that one out) plus a 3x2m plant space with all the gubbins in there. We built it for ourselves but given it also acts as the building foundation and complements the other spaces in the house so should add value and appeal to a future buyer if we ever have to. Planners also did not blink, were only concerned with the above ground massing and volume increase.

 

1 hour ago, puntloos said:

 

Main goal for basement is to 'hide away' noisy or bulky stuff and make the garage usable for actual cars, should the need arise. 3x4 is the minimum. 5x5 seems perfect.

Anything beyond that adds to the stuff we don't really need, so unless the next sqm would be almost near free I don't think we'd do it? Or am I being shortsighted? (of course there's also a budget to think of..)

 

 

If you're solely using it for 'stuff' you'd put in the garage then I'd think carefully about your ROI. Do you mean plant like MVHR, etc? That may be more of a justification if it keeps other parts of the house uncluttered.

 

1 hour ago, puntloos said:

Not sure what you mean.. clearly an actual room-in-the-garden would eat garden space, and we are VERY tight on that, we'd love a larger garden than we have, this already is a sad compromise... 

 

Hm? Not sure why not? Both our actual garden room, a theoretical extension later, or a basement need some PP? 

 

I sense I'm missing your point...

 

Garden rooms (log cabins, shepherd huts and the like) are usually allowed under PD providing they meet the requirements (height, 1m separation from boundary and % of land occupied etc). Do a basement now or forget about it, they are horrifically expensive to retrofit and only make sense in areas (like west London) where the per m2 property values can justify them.

 

1 hour ago, puntloos said:

Fair. My initial idea was literally copying the basement one level down. 

But I figured that if a basement is harder to build if you're close to the neighbours, why not move it more centrally.. but I can see the point of having walls align etc, so perhaps the best mental model is to have it straight below the hall (also less weight, since it's fully open above?) which is 5.8*3.5? 

 

Some people (maybe you?) suggested to do a full basement somewhere (140-odd sqm!) but I doubt that'd pay off, unless somehow the cost of e.g. the foundation would disappear.. 

 

Yes, foundation cost would disappear as your basement would take that role. Only a SE, after analysing the ground investigation report, could advise whether a centrally located basement would complicate the foundation and slab design massively. I'd guess the concern would be that your basement box moves independently of the rest of the house, so you'd likely be looking at a raft foundation tied to the basement box so its one contiguous structure.

 

Proximity to neighbours is indeed is a complicating factor (party wall and site logistics) but if you're doing classic foundations in clay then I'd expect you'll hit many of the same issues. What convinced us was when next door had to go down 2.5m when doing a modest side extension and we realised that worst case (we are clay over gravel over chalk) we'd do the same and a basement was really just scooping out the bit in the middle. This was before we discovered raft foundations but they can still need piling if there is risk of ground movement.

 

1 hour ago, puntloos said:

 

Idon't think I've gotten to this part of house building theory yet ? not sure if this is the time/place but can you be slightly more specific? 

 

Think I've covered it all above - no expert other than have done it once and learned as I went  BTW, architect thought we were crazy - predicted a damp space, rarely used and a horrific risk of cost overrun.

 

It is warm (no heating), spacious, came in bang on budget and is the feature of the house everyone wants to see. He did admit afterwards that he was wrong and now wonders why everyone doesn't do them

 

 

 

[puntloos]

Just called a basement guy. Their handwavey quote for a 5x5 basement was 20,000. I wasn't 100% clear on if it's including or excluding excavation and removal (I suspect ex.)

 

He also noted it might be better to do a Non-material amendment after PP, so planning team doesn't take e.g. living space in basement under deep consideration...

 

3 hours ago, Bitpipe said:

If you're solely using it for 'stuff' you'd put in the garage then I'd think carefully about your ROI. Do you mean plant like MVHR, etc? That may be more of a justification if it keeps other parts of the house uncluttered.

 

Nono the primary reason is being a plant room. Noisy/bulky Stuff.

 

3 hours ago, Bitpipe said:

Proximity to neighbours is indeed is a complicating factor (party wall and site logistics) but if you're doing classic foundations in clay then I'd expect you'll hit many of the same issues. What convinced us was when next door had to go down 2.5m when doing a modest side extension and we realised that worst case (we are clay over gravel over chalk) we'd do the same and a basement was really just scooping out the bit in the middle. This was before we discovered raft foundations but they can still need piling if there is risk of ground movement.

 

Yup. It might make a lot more sense for the basement guy to do the full foundation with the basement right under the hallway.. and then discuss if we want to go full-basement