Request for an advice on 1 storey with full height basement garden house (7x11m)

[Daniel]

Hello

 

I'm going to build a one storey garden house with basement this summer. I haven't really build a lot before so I would appreciate an advice here. The site is very tight and one of the objectives of the project is to utilise as much space as possible efficiently, so every inch of the wall width counts here. I'm going to build it mostly myself with one assistant builder and have to squeeze the project into a lowest possible budget.

 

The building plan as very simple being effectively just a box of 7.5m x 11.5m with basement and 1st floor both 2.5-2.7m tall. There will be one internal non-bearing wall and a flat roof.

 

1) Basement walls and ICF

ICF blocks seem to be hugely advertised nowadays by I'm not sure is there real value behind it? Self-building seems pretty straight-forward especially after studying manuals.

I'm considering the possibility of building either basement walls of ICF and first floor of SIP and frame or building both basement and first floor of ICF.

Does anyone here have experience with them? Should I really be using them especially in terms of saving precious centimeters of the wall thickness while achieving sufficient  U-value 

There are quite a few ICF suppliers on the market, which ones are cheaper and still good quality? I've requested a quote from Nudura (and studied their docs quite thoroughly) but expect the quote to be quite high

 

If not ICF that which other options should I consider for basement walls?

 

What would be your opinion on the thickness of these walls. I know people are mostly using 8" and more thick concrete for basements, by do you think it would be technically possible to go with 6" by adding extra rebar? Or even 4". I just must save every extra inch, that's crucial

 

 

2) First floor walls, roof and SIP

 

I was thinking maybe I should build everything higher than the basement of SIPs? Including the roof. Am I right that I wouldn't need vertical steel supports for SIPs in such a case?

Which other ways for building first floor and roof should I think of? It should be space efficient. Also I'd better save on extra labour in favour of pre-build units like SIP.

 

 

 

 

 

I'd be glad to provide any additional information needed..

 

Thanks!

 

 

 

 

 

Edited May 14, 2017 by Daniel

[RichS]

Re. the roof in SIPs.

I got some quotes for mine, supply only, and they were eye watering. Regardless to say I won't be using it.

[PeterW]

Welcome ..!

 

i doubt you will get a SIP that will span 7m - that will need some serious support and an 11m steel will be even more eye watering ..!

 

Looking at that design I would consider ICF all round - easier and quicker especially if you have room to dig down to get them in with space for waterproofing below ground. 

 

At 154sqm that is a big "garden house" and has the ability to swallow £150-200k at a blink if you're not careful ..! 

 

[Ferdinand]

@Daniel, welcome.

 

I am not sure what you mean by 'build this summer', but that will need planning permission and it could take 12 months at least to design, get planning and build - more likely longer. And depending on your garden you could get questions from neighbours -overlooking etc due to the 2 story construction if your basement is not entirely submerged.

 

One way to get it more quickly would be design and build from a single company that know the ropes.

 

If you plan to use it this summer or autumn then you may be best going for something under 30 Sqm which does not require planning. It may still be a struggle.

 

Ferdinand

Edited May 14, 2017 by Ferdinand

[mvincentd]

I was absolutely determined to use icf, insisted the SE calcs and drawings were done based on Nudura, and went on the Nudura 1 day course.

To cut a long story short I tried my best to resist every argument against it and wasted a lot of time as a result, but in the end could not ignore the risk it represents when used in a basement scenario.  Talk to surveyors that do lots of remedial work on basements.

Also if you want a guarantee thats worth having from a waterproofing system expect to pay plenty......ask for a quote for icf versus maybe in-situ RC and spot the difference!  If you're using every inch of your plot how will you safely put a man between your excavation and the icf to apply an external waterproofing system.

Your ground type will likely steer the best system for you.

Above ground i'd use icf happily.

 

 

[Mr Punter]

I have done an icf basement.  Used Polarwall with 300mm concrete core reinforced with mesh.  You will need at least 800mm of working room around the outside.   Potential issues are Party Wall notices, Means of Escape, ventilation, daylighting, excavation and temporary propping / shoring, engineering design and calcs, waterproofing, warranty guarantees and final value v. value of above ground floor space.

 

As you are a novice on a tight budget I advise that you steer clear of a basement.

[Daniel]

8 hours ago, mvincentd said:

I was absolutely determined to use icf, insisted the SE calcs and drawings were done based on Nudura, and went on the Nudura 1 day course.

To cut a long story short I tried my best to resist every argument against it and wasted a lot of time as a result, but in the end could not ignore the risk it represents when used in a basement scenario.  Talk to surveyors that do lots of remedial work on basements.

Also if you want a guarantee thats worth having from a waterproofing system expect to pay plenty......ask for a quote for icf versus maybe in-situ RC and spot the difference!  If you're using every inch of your plot how will you safely put a man between your excavation and the icf to apply an external waterproofing system.

Your ground type will likely steer the best system for you.

Above ground i'd use icf happily.

 

 

 

 

Hello

Could you please drop some light on risks of using nudura for basements? 

The project is going to be more of a diy type and I want to avoid having extra workers involved as much as possible, that's why the idea of the blocks is so appealing.. though the quote on them and accessories seems to be quite not very cheap, I hope to "return" the investments by not paying others (this type of approach suits those who have nothing else to do anyway.. like me at the moment)

 

How to put a man in between the excavation and icf that's what I'm  still thinking about. My wife is in charge of talking to neighbours 

 

For waterproofing I was going to use waterproof concrete, stick and peel / or spray paint rubbery paint and drainage membrane accompanied with a drainage pipe along the perimeter covered with gravel. I hope this will work

 

 

 

 

 

 

 

 

 

 

 

 

 

[Daniel]

17 hours ago, RichS said:

Re. the roof in SIPs.

I got some quotes for mine, supply only, and they were eye watering. Regardless to say I won't be using it.

 

Based on prices on SIPs from this page (http://www.supersips.uk.com/structural-insulated-panels-prices.htm) I think I probably should consider buying instead OSB sheets (around 7 pounds per sq.m.) + separate eps sheets (8-10 pounds per sq. m.).  That could make it twice cheaper. And longer.. Which other constructions should I look at? Thanks!

[Daniel]

25 minutes ago, Mr Punter said:

I have done an icf basement.  Used Polarwall with 300mm concrete core reinforced with mesh.  You will need at least 800mm of working room around the outside.   Potential issues are Party Wall notices, Means of Escape, ventilation, daylighting, excavation and temporary propping / shoring, engineering design and calcs, waterproofing, warranty guarantees and final value v. value of above ground floor space.

 

As you are a novice on a tight budget I advise that you steer clear of a basement.

 

 

Hi

 

Was it a basement conversion project or a new build? Just wondering about 300mm thickness, how many floor upstairs are you basement walls holding? I've found an engineer but haven't given him a specific task yet, until things are more or less settled down in my own head.. He estimated roughly that 250mm would be probably enough, though I really hoped for 200mil

 

And btw why did you choose polarwall? I'd appreciate if you could tell me what was a price per sq.m. according or simply pm their quote so I could compare with other suppliers. And how did you waterproof btw?

 

Thanks

 

[Daniel]

15 hours ago, Ferdinand said:

@Daniel, welcome.

 

I am not sure what you mean by 'build this summer', but that will need planning permission and it could take 12 months at least to design, get planning and build - more likely longer. And depending on your garden you could get questions from neighbours -overlooking etc due to the 2 story construction if your basement is not entirely submerged.

 

One way to get it more quickly would be design and build from a single company that know the ropes.

 

If you plan to use it this summer or autumn then you may be best going for something under 30 Sqm which does not require planning. It may still be a struggle.

 

Ferdinand

 

Hello Ferdinand

 

All planning and neighbours questions are being dealt with by my wife and very fortunately she has quite an extensive experience in both. I think will be able to start building by the end of the summer 

 

 

[Daniel]

16 hours ago, PeterW said:

Welcome ..!

 

i doubt you will get a SIP that will span 7m - that will need some serious support and an 11m steel will be even more eye watering ..!

 

Looking at that design I would consider ICF all round - easier and quicker especially if you have room to dig down to get them in with space for waterproofing below ground. 

 

At 154sqm that is a big "garden house" and has the ability to swallow £150-200k at a blink if you're not careful ..! 

 

 

Hi Peter

 

The 7.5m span is a real concern at the moment. I hoped to avoid steel and welding

ICF all round seems looks like a considerable option. I though of alternating the concrete core width and using taper forms as a ledge for joists in the case of allaround ICF

 

 

 

Speaking about 7.5m span:

does anyone have experience with laying joists over such a distance? I've checked I-wooden joists, LVL beams, charts for regular lumber - the depth (height)  necessary seems to be around 35cm. Which is not space saving at all. If i got everything correctly. That's for overall load of 200 kg/m2 for both the floor and the roof. So I'm now a bit confused 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[PeterW]

It's the span that is causing you the problem not the weight. You will have to go deep to get the deflection limits hence the depth you are seeing. 

 

I would look at putting some sort of stub walls at least to get a mid span down to say 4m and then use that to support the roof lengths at 5.5m

[Mr Punter]

2 hours ago, Daniel said:

 

 

Hi

 

Was it a basement conversion project or a new build? Just wondering about 300mm thickness, how many floor upstairs are you basement walls holding? I've found an engineer but haven't given him a specific task yet, until things are more or less settled down in my own head.. He estimated roughly that 250mm would be probably enough, though I really hoped for 200mil

 

And btw why did you choose polarwall? I'd appreciate if you could tell me what was a price per sq.m. according or simply pm their quote so I could compare with other suppliers. And how did you waterproof btw?

 

Thanks

 

 

New build with timber ground floor, so partially propped.  Chose Polarwall as it is flexible and simple to construct.  Waterproofing was concrete admixture plus type c internal drained cavity, sump and pumps.

 

Ground was chalk and putty chalk.  Polarwall materials were £5,600.  Area was 66m2 internally but including a light well - before we added the internal wall linings.  We also had slab, mesh, temporary works (augered and king post walls) and additional insulation.  In total the basement structure alone was £56,000, waterproofed and insulated.

[le-cerveau]

My house (design, just starting build) had 12m spans in it.  The only way to do it was to break up the spans with an RSJ (with a post in an internal wall) so that 8m concrete planks could be fitted, resting on the RSJ, so the max span is 8m of concrete planks onto the RSJ, which gives me the large spans.  The Concrete planks are 250mm thick with a 30mm max camber in the centre.

[Bitpipe]

I have a basement as part of our new build, it is 11.5m x 10.5m and constructed as an 'open box' i.e no lid. Passive timber frame house sits on top, basement is passive also (fancy way of saying it sits on a foundation of EPS and walls are clad in EPS, meeting the outer leaf and insulated section of the timber frame. Three large 10m steels span the ground floor, (one on a post) with a web of smaller steel joists taking point loads from above and web joists in-between. We could have had a solid walls in the basement but wanted flexibility in the layout.

 

Some quick comments on your plan.

 

In my experience. the cost of a basement is dependent on a number of features. Getting planning is by far the easiest bit

 

1) most fundamentally - ground conditions. Tricky conditions such as made ground, hard rock, chalk (solution features) high water table etc will drive up excavation costs and construction costs. We have chalk under gravel (Thames valley river bed) so needed a very substantial slab (300mm) with lots of reinforcement.

 

The only way you are going to know what the required basement spec is, is to have proper ground investigation (cores to 4m and probes to 10m) at 2-3 points in your footprint.

 

You then need to have a SE work out the required structure, concrete, steel etc. You may get an early view on what's likely under your feet by searching for nearby historical boreholes to get a feel, but you'll ultimately need to do your own investigation as conditions can rapidly vary.

 

Water table will dictate your degree of waterproofing. For us, water table was low at 6m so we were able to use warrantied waterproof concrete on its own. Our friends built near the Thames and needed external tanking and wp concrete (they used the Glatthar system, good but not cheap). Some opt for the internal membrane, sump & pump. Principal here is that you build a leaky box, allow the water to safely collect in a sump and continuously pump out. Very common on retrofit basements in London.

 

Budget £5k for the investigation. If your LA adds requirements for contamination surveys etc then expect to pay a bit more. SE will vary, we paid £5K but got quite a bit of additional work in there too (services design etc..).

 

BC will then want to ensure you have means of escape and/or fire suppression so external stairs or a sprinkler system will need to be in the design.

 

Will you have wet services down there? If so, you'll need to pump wet waste up to the main foul level. How are the internals being lit? We used UPVC windows and GRP light wells from MEA - they've been very effective and the concrete team only needed to leave the aperture (sufficiently reinforced obviously per SE design).

 

Party wall is critical also, we were lucky in that we escaped any notification due to the 45^o rule. We were within 6m of one neighbour and 8m of another.

 

Have you done any of this investigation & design yet? Pretty impossible to cost the job without it in my opinion.

 

2) Design - a simple rectangular box is cheapest, thinner the raft & walls the cheaper (subject to SE spec). Penetrations will add cost as they complicate the formwork and require more prep before the pour.

 

3) Access - a very tight site can be expensive to excavate, muck away and to get steel and concrete onto. You need min 1m working space, with appropriately battered back walls around the basement. If your ground is very soft or loose, you may need to sheet pile (very expensive). Our excavation (not much bigger than yours) required 73 20t trucks to cart away the spoil. Machine was loading them directly so it only took 3 days - we were lucky to have good access so this was not too painful. We also pumped concrete for the slab and used shuttered runs for the walls (pump hire is expensive) direct from the mixer.

 

4) Build method. ICF is a fine choice, especially if you're using an external or internal waterproofing method. If you're reliant on just WP concrete then you need an excellent pour with no honeycombing and this is impossible to confirm with ICF so traditional formwork is a better option. You can DIY your waterproofing but it will not be warrantied. We used a SIKA system which had admix in the concrete and the water bar between day joins - the SIKA rep came to site to inspect the work before pours and the team photographed everything as they went. So we now have a 20 year guarantee on the integrity, upon which the building warranty is dependent.

 

Cost for our 120m2 basement (including demo of the existing and services) was £120k in Berkshire - probably £90-100k purely for the basement itself if you strip out the other parts of the package. We used a reputable local groundwork who brings in a proved team that did the steel, formwork and pouring - goes without saying that it's pretty skilled work.

 

Good value for money in my opinion given the extra space that we acquired. Basements do not need to be scary but there is a lot of prep that you need to do before you can really understand and mitigate the costs.

 

Fair to say that Tony (of Tony's house) did his own basement DIY at a fraction of my cost (he is an experienced builder of 30+ years) and I went to see it - very nice it is too.

 

Probably plenty more to share on our experience if you have more questions!

 

 

[Daniel]

7 hours ago, Bitpipe said:

I have a basement as part of our new build, it is 11.5m x 10.5m and constructed as an 'open box' i.e no lid. Passive timber frame house sits on top, basement is passive also (fancy way of saying it sits on a foundation of EPS and walls are clad in EPS, meeting the outer leaf and insulated section of the timber frame. Three large 10m steels span the ground floor, (one on a post) with a web of smaller steel joists taking point loads from above and web joists in-between. We could have had a solid walls in the basement but wanted flexibility in the layout.

 

Some quick comments on your plan.

....

 

Wow that a lot of extremely useful information, very much appreciated, I'm making notes here.. 

 

 

Btw, have anyone heard of PWF-SIP (pressure treated SIP foundation)?

 

 

Edited May 16, 2017 by Daniel

[PeterW]

3 hours ago, Daniel said:

Btw, have anyone heard of PWF-SIP (pressure treated SIP foundation)?

 

Not seen them in the U.K. but they are used in Canada - don't think they've got a BBA certificate for U.K. use. I'd be vary wary putting timber below ground as whatever you do to it it will rot eventually. 

[Ferdinand]

23 hours ago, Daniel said:

 

Based on prices on SIPs from this page (http://www.supersips.uk.com/structural-insulated-panels-prices.htm) I think I probably should consider buying instead OSB sheets (around 7 pounds per sq.m.) + separate eps sheets (8-10 pounds per sq. m.).  That could make it twice cheaper. And longer.. Which other constructions should I look at? Thanks!

 

You would the need a SiP manufacturing press costing some 10s of thousands (guess), and the place to put it, and the people to run it. SiPs work because they are bonded together under pressure.

 

Steel, glass, and rubber is cheaper than a car, but then you have to pay for the factory :-).

 

If you dig around on eg ebay there are some small businesses making SiPs, though. One I looked at was farm-based.

 

Ferdinand

 

Edited May 16, 2017 by Ferdinand

[PeterW]

58 minutes ago, Ferdinand said:

 

You would the need a SiP manufacturing press costing some 10s of thousands (guess), and the place to put it, and the people to run it. SiPs work because they are bonded together under pressure.

 

Steel, glass, and rubber is cheaper than a car, but then you have to pay for the factory :-).

 

If you dig around on eg ebay there are some small businesses making SiPs, though. One I looked at was farm-based.

 

Ferdinand

 

 

SIPS are usually foamed in situ, not glued. It is PUR in them as its structurally stable, not EPS which is not stable in shear or tension. 

 

@DanielYou "could" make your own SIPs, by the time you've got an SE to sign off the design and found an insurer that may accept them, you will have spent twice as much on them than buying them in...

[Bitpipe]

On 5/16/2017 at 03:35, Daniel said:

Wow that a lot of extremely useful information, very much appreciated, I'm making notes here.. 

 

Happy to help. I must have spent two plus years researching and designing our basement (it's actually how I stumbled across e-build, predecessor of this site).

 

Unlike most other building decisions, a lot of the basement cost is dictated by your local circumstances - ground conditions, site, design and budget.

 

When you know all of those factors you'll be able to accurately cost, until then it's guesswork and be warned that if you start work without absolutely certainty then you could face a  steep increase in costs.

 

Quote

Btw, have anyone heard of PWF-SIP (pressure treated SIP foundation)?

 

By all means investigate possible build methods but until your SE and BC have signed off on your design, you'll not know for certain what you need.

 

At one stage of our investigations, there was the potential for piling which would have killed the budget, luckily another round of GI allowed that to be eliminated as a possibility (I say luckily, the new GI survey cost anther £3.5k.....)

 

[mvincentd]

On 5/15/2017 at 09:44, Daniel said:

Hello

 

Could you please drop some light on risks of using nudura for basements? 

The project is going to be more of a diy type and I want to avoid having extra workers involved as much as possible, that's why the idea of the blocks is so appealing.. though the quote on them and accessories seems to be quite not very cheap, I hope to "return" the investments by not paying others (this type of approach suits those who have nothing else to do anyway.. like me at the moment)

 

How to put a man in between the excavation and icf that's what I'm  still thinking about. My wife is in charge of talking to neighbours 

 

For waterproofing I was going to use waterproof concrete, stick and peel / or spray paint rubbery paint and drainage membrane accompanied with a drainage pipe along the perimeter covered with gravel. I hope this will work

 

Well during my risk assessment of using icf in a basement I spoke with various people who collectively left me with sufficiently diminished confidence in it that I moved to RC.  That's all about my personal risk threshold...yours might differ.  I suggest you speak with engineers, surveyors, builders and particularly waterproofing experts.