Ideas for foundations for wooden sumerhouse

[wytco0]

I have a house with a large(ish) garden and it has a summerhouse on it next to a river. The summerhouse is at least 70 years old but is derelict and near to total collapse.

I know that during WWII it was used to house a family! Its only a single room and I would guess that its about 5mx4m but I havnt measured it yet.

Its about 4-5m tall with an apex roof and it did have a small lean to kitchen on one end but that fell down years ago.

I want to replace the summerhouse with something of similar dimentions and design.

As far as I can see the current building has no foundations at all, the upright wooden corners seem to sit straight on the ground.

As the summerhouse is built on a riverbank and the riverbank has several large trees with big roots, I would like to build the replacement summerhouse with as little footings as possible so that I can minimise damage to the trees.

As I know almost nothing about foundations for buildings I am looking for ideas on a what options exist for providing a firm base for the new summerhouse.

Thanks.

 

[wytco0]

Any ideas on this? are there any options or are normal footings the only options?

I am sure I read something about using alternatives somewhere a while ago but I cant find it.

 

[Deluks]

Depends on what the grounds like, or how heavy is a barrow of rocks?

I'd wager concrete slab with reinforeskinment.

 

[wytco0]

Well the ground is full of tree roots and is on a river bank soil around here is chalk. I am trying to avoid using reinforced concrete, I am looking for other options which are less invasive.

Its going to be a wooden summerhouse and the current one apears to have no foundations at all!

 

[PE]

The problem may be getting a non concrete base level enough. If its not totally level then the summerhouse will potentially move and you may get stress issues on the wood etc. When we had aour 4.5 x 3 summerhouse installed it was stressed at several different times that the base would need to be level and firm and concrete was the most efficient way of achieving this, although patio type slabs could be used aswell

I have seen summerhouses on a framework of sleepers and also some of the wooden buildings use piles into the ground which is possibly a good solution for uneven ground as well as brick piers maybe?

Do a google on pier foundations, strip foundations and you should get some more ideas

Sounds like a nice retreat next to the river

 

[wytco0]

Do a google on pier foundations, strip foundations and you should get some more ideas

Sounds like a nice retreat next to the river

PE thanks for that inof, found some usefull info on pier foundations.

It is a lovely spot, with otters in the river !

 

[Jasonb]

If you don't want concrete then then you could consider driven piles or screwpiles though both are not really DIY options and would work out quite expensive for the small amount you require. Hand dug or auger drilled piles are a possibility but not easy in chalk.

If the chalk is quite close to the surface then you could go for pad foundations, should only need about six for your size structure. These would be approx 750mm square with 150mm conc in the bottom, build up with dense concrete blocks laid flat, then timber beams and joists onto of these. I did this deck in a similar way but stopped the blocks just below the turf and toped it off with rocks. Another way to do the piers is to pour concrete into large "cardboard" tubes which are approx 300mm dia. Both methods would use a minimum of concrete.

Jason

 

[wytco0]

If the chalk is quite close to the surface then you could go for pad foundations, should only need about six for your size structure. These would be approx 750mm square with 150mm conc in the bottom, build up with dense concrete blocks laid flat, then timber beams and joists onto of these. I did this deck in a similar way but stopped the blocks just below the turf and toped it off with rocks. Another way to do the piers is to pour concrete into large "cardboard" tubes which are approx 300mm dia. Both methods would use a minimum of concrete.

Jason

Hi Jason sorry for the delay in replying. I dont think I want to go down the piles route for this building but I am using that on a house being bult for me.

I am very interested in this photo from your site http://smg.photobucket.com/albums/v156/jasonballamy/Oast Deck/?action=view&current=s1.jpg the summer house I want to build is a is a simpler version of this, it will have an oak weatherboard facing and a softwood frame probably with a galvanised corrugated iron roof which will look very similar to the existing summerhouse (which has lasted at least 70 years).

How did you do the foundations for your building? I expect mine will be much lighter.

 

[Jasonb]

First I maust say that someone else did the "foundation" I would not put blocks down as badly as that.

This was actually a bit of a way round a planning issue, there was an old mobile type home in the same place which the planners were willing for the client to remove but did not really want anything put back. The problem was got around by reducing the ground level, putting the old mobile home chassis in at the new level then laying joists and a ring beam on that which was stabalised with some blockwork piers.

Just built the structure off that, basic oak frame with studwork infill.

You could set some saddle stones on small pad foundations to keep the concrete to a minimum and then set your oak frame on them, often used for storage barns as the stones make it harder for vermin to get in, like the third pic down here

Jason

 

[wytco0]

First I maust say that someone else did the "foundation" I would not put blocks down as badly as that.

Just built the structure off that, basic oak frame with studwork infill.

You could set some saddle stones on small pad foundations to keep the concrete to a minimum and then set your oak frame on them, often used for storage barns as the stones make it harder for vermin to get in, like the third pic down here

Jason

Hi Jason thanks for the ideas, I think I am getting close to a solution, I will probably go for some small concrete 'pads' in the corners to provide a level and then use some slabs/blocks on the earth to provide additional support for the joists and spans.

Although I cant see the foundations in the building I am replacing I am pretty sure they don't exist, it looks as though its just 6x6 inch corner posts on the earth.

Here are a couple of photos of the current Summerhouse that I want to rebuild/replace.

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[Jasonb]

Does look as though its reached the end of its life, I think the undergrowth is whats holding it up

Keep us posted of progress and feel free to ask any questions.

Jason

 

[wytco0]

I will be up there later today and I am going to have a look at the old summerhouse and try and get a definitive answer to what sort of foundations it currently has (I think the answer will be none).

In the next couple of weeks I am also going to be looking into buy in the timber for the rebuild and I am after a bit of advice on the likely costs and the best way of buying it.

I would like to use a local timber yard at least for the softwood I will use for the beams, studwork, roof and flooring etc. I am hoping to use Green Oak for the weatherboards but I am not sure If I will be able to find anything like the current boards locally.

Does anyone have any idea how much I should be paying for timber? I will use current standards sizes as I suspect the imperial sizes wont be so easy to get.

The biggest bits I need will be the corner posts which are currently 6x6Inch by about 3 Meters, are posts that size easy to get hold of?

One last question (for now), I will probably insulate the new building as far as I can, for the walls I was thinking that I could do this by using something like sheep's wool or processed paper to fill the frame, I would use a weatherproof barrier under the outer weatherboard, however I am not sure what to use for the floor and the ceiling? I would probably leave the loft space cold. Does this make sense or should be I be doing something else?

 

[Deluks]

Just a few more ideas into the pot...

Lots of questions there, which means you have quite a bit to learn yet, which means you shouldn't go and buy anything until you have the 'plan' properly sorted and given the green light by the wise ones on here

Oak is pricey, very pricey compared to standard softwood cladding. Your 6x6 posts will be expensive, you can do it with 4" posts instead.

Don't bother insulating the walls if you won't be insulating the roofspace.

If you want to splash out on the wall construction, you can use breathable roofing felt over the framework, before adding vertical battens, then the cladding. This will give a weatherproof yet breathable structure, and should be strongly considered if you plan to insulate. Building paper is the traditional method of achieving this, but isn't as durable as modern underfelt such as tyvek, and isn't that much cheaper.

Sheeps wool is enviro friendly and fairly efficient, if you can get 4" in the walls, and a bit more in the roof then all good, but the underfloor will need insulating as well for you to really feel the benefits. not sure sheeps wool would be ideal for this, maybe polystyrene.

Unless you plan to heat the space, you will feel more benefit from insulation in the summer, to help keep the heat out. It could be done at a later date if you leave the internal studs bare for now.

 

[wytco0]

Deluks,
firstly sorry for the long delay in replying.

In fact I have still not done anything about the summer house as I got a fright when I started to look at the cost of oak for cladding. I am certainly going to use softwood as the current summerhouse has lasted 70+ years and is made from 100% softwood.

One thing I did confirm, the current summer house does have some sort of basic foundations, the corner posts rest on a pads about 4 inches below the ground level that looks as though they are made from a mixture of rubble lightly held together with cement !

You are right I definitely have a lot to learn but this seems to be a great place to find people to ask.

Your suggestions are very helpful and have given me a lot of ideas. Thanks very much

 

[wytco0]

I think the Summerhouse rebuild is going to start soon.

The builder started work on our new house in March in order to make sure our planning permission did not run out and its inspired me to have another look at the summerhouse, that and the fact that the existing structure is now leaning at an alarming angle !!

A couple of weeks ago I used a post hole auger to make a 6 inch wide hole about 1.5m deep next to the summerhouse. I had expected to hit the chalk at that level but instead I was still in good quality silty soil, As this is only a few meters from the river I suspect that the riverbank may have been wider and that it used to flood prior to the banks being altered many years ago.

So I am back to thinking about what sort of foundation to use, I still want to insure that it does not damage the trees and I don’t want a full slab but I am worried that my earlier conclusion that I could dig 6-8 holes and make some simple pier foundations may not work as the soil is not very compacted and the chalk is further down than I had thought. Against that the existing building has stood for a long time with far less substantial foundations that that.

I have seen some square concrete pads with screw thread at the top that allow for a sub-frame to be attached and also allows some height adjustment the trouble is that I can’t remember what they were called or where I saw them, they looked as though they might work well on top of my piers. Anyone got any idea what they are called?

As to the rest of the building I am almost decided that it will be mainly a softwood frame with 4x4 corner posts and a simple frame for the rest of the walls. I will insulate all the walls the floor and the roof and I am thinking of putting in a solar PV lighting system and a wood burning stove. I am currently undecided on whether to use softwood painted weatherboard or whether to use oak for the cladding. Roof will probably be galvanised Corrugated Iron (because I like it) but I notice that there are several bitumen type sheeting options now, anyone got any comments on them as roofing?