Ideas for foundations for wooden sumerhouse

[customtimber]

Hi,

The adjustable pads are on this website

http://www.thegardenroomguide.co.uk...ration-of-garden-room-foundations/2010/03/12/

Im not sure on cost but to be honest as long as your block work is level and square in the first place then you should not need them. With regards to the foundations since it near to a stream that may/may not rise we generally dig down to the water table and install a full rebar cage and infill with concrete this general go's the whole width of the face of the building plus returns at both end to tie back this prevents the weight of the building causing subsidence. ignor previous if at least 1.5mtr from bank . If you are doing pads and subframe then be sure to use 'Solid' concrete blocks NOT 'Dense' (these will crumble under pressure).

If required i can provide you with a Pads and Subframe plan if you provide floor dimensions of building.

Hope this is some help.

 

[wytco0]

customtimber, thanksfor that info those are almost the same as the ones I saw before and actually look better.

The Sumerhouse is about 5 meters from the bank and I am going to put the replacement a couple of meters further back than that so it will be about 7-10 meters from the bank.

Interesting info about the foundations you use, I am hoping to end up with a lightweight foundation and based on the life of the existing building I hope I can get away with it.

 

[customtimber]

We use a variety of footings depending on ground conditions you mentioned that you had done a test hole and soil was soft and did not hit chalk for some depth. to give you some comparison the foundations we use on our 9mtr square buildings consist of 38 1mtr cube concrete footings with solid block work on top this complys with building regs and over what is needed on weight ratio. on our smaller builds we general dig down till we hit solid ground (very difficult to hand dig) then infill with concrete and set 'PADS' (9"sq solid concrete block) on top these never span more then 6ft apart (using a 6" Tan Subframe) or 3ft for 3" subframe.

I remember you saying you want minimal interference with possible tree routes unless trees have a 'TPO' on them or building is proposed to be really close we generally advise to move buildings so if route system is found we only remove the smaller routes causing little to no damage on the trees. If your ground is so soft down to 3ft you will not have much choice but to use concrete or 6x6 tan sunken posts. In the end i have had customers who have 'scrimped' on the footings and damaged the building because one or more corners have sunk in which case they have had to pay us to come out and underpin the whole building.

Let me know your thoughts and if more info needed just ask.

 

[wytco0]

Customtimber, thanks for the additional info.

The test hole I dug was about 1.5m and that was the deepest I could go with the hand auger I was using (and to get that deep I had to dig a hope about .5 m so that the auger handle would work below ground level!

However I know that the riverbed is chalk and I don't think it can possibly be much more than another 1m or so deep.

If I can get down to the chalk would I be OK putting a concrete pillar straight on top of that? I know that the hole would be below water level at that point as I hit water in my test hole. I am not sure how to use concrete under water.

I think I will have another go at the test hole and see if I can get another metre or so down, anyone know how to extend a hand auger

 

[customtimber]

Hi,

What is the L,W,H of the building and what is to be made from and what being stored in it? To be honest if you have gone done 1.5mtr X 0.5 diameter then depending on the answer you will more than likely be over the top all ready! With the holes you will be either able to you 8"x8" post with rebar spikes or rebar and concrete pour. Working with concrete at the water table is not a problem and can be overcome very easily.

Let me know the answers and i will do some calculations and let you know the best solution.

Thanks.

 

[wytco0]

Hi Customtimber,

H 4.8m (ground to apex of roof)

W 3.5m
L 5m and there is a 3m leanto extension on one end which is 2.8m at the highest point.

It will be built of timber with a corrugated iron roof, I am planning to insulate all walls the floor and ceiling.

It will mainly be used as an office and will not have very much in it desk some chairs a small wood burning stove etc.

There are photos on page 1 of this thread showing the existing building.

Many thanks for your help on this.

 

[customtimber]

Hi

I havent forgotten about plans my guy that does structual calcs for my company is on leave but he is doing a couple of bits for me at home so i will be in contact. i do know that 1.5mtr to max 2mtr depth is ample, is just the distances between to spread the loads evenly i am waiting for.

thanks

 

[wytco0]

Hi

I havent forgotten about plans my guy that does structual calcs for my company is on leave but he is doing a couple of bits for me at home so i will be in contact. i do know that 1.5mtr to max 2mtr depth is ample, is just the distances between to spread the loads evenly i am waiting for.

thanks

OK thanks no great hurry as it will probably be August before I can start this. Thanks fro your help.

 

[wytco0]

Well I still haven't started the summerhouse replacement but I am soon going to have to demolish the existing building as its dangerous.

Can anyone advise me if I face any planning problems with this summerhouse, I wasn't planning on asking for permission as I was going to rebuild to look the same as the exiting building in the same place and the same size.

Now that I have to demolish the existing building and wont replace it for a while (some months I think), I am worried that i could end up with planning problems.

I still haven't decided how to handle the foundations either but I think the most likely solution will be concrete pads.

 

[wytco0]

Guess what I still haven't started the summer house rebuild !!!

Just starting to think about it again, we had to demolish the old building as it had become dangerous and we were worried about visiting children playing in it and it falling down on them.

I was looking at regulations on summer houses/garden buildings and I noticed that there is a limit of height of 4m for summerhouses without planning permission, the original building was 4.5m high. Will I have to obtain planning permission of can I rebuild to the original dimensions?

Thanks.

 

[leew2]

If you have completely demolished the old building then you will need planning permission to rebuild it even if it is the same size and appearance as to what was there before. As there was an existing building on the site there is a good chance permission will be granted but cannot be granted.
If the building is under 4m high then it is 'permitted development' and does not need planning permission in most cases (it also needs to be more than 2m from a boundary, less than half the garden covered in buildings and not in the garden of a listed building or on 'designated land').
Planning permission does not cost much relative to the cost of the building thus it would be a good idea to apply, in the unlikely chance it is rejected then you will just have to build it under 4m.

 

[David P]

I just came across the thread and thought I should say that I spent a while agonising over the same decisions too.

In the end I did a load of historical research into what people used before 1847 (when cement as we know it was invented) and came across quite a few options. for such small buildings most of these involved laying freestone onto a very well tamped soil as level as possible, and wider than the wooden plate used to spread the weight - same principle used for many cathedrals.

It seems that there was a shift of thinking with the invention of concrete that stopped builders thinking of the entire wooden structure as a floating coherent form, much like a boat, to a series of sticks propped upon a rigid rock.

The choice that I made was to go with an old technique that involved;
1 digging a shallow trench to undisturbed soil and tamping till there was no more movement.
2 laying a 6inch bed of course gravel into the trench
3 laying fairly substantial oak beams on the gravel -- these were deeply charred on the surfaces at bottom and side to prevent rot (the gravel lets water drain too).
4 the structure is then fixed to this floating base frame. the main posts being morticed and dowelled into it.

This way the base frame has the effect of averaging out any local movement in the soil (tree roots growing and rotting away) - if any short stretch of ground subsides the gravel shifts to accommodate the averaged weight - so a 3 inch drop of level in one place translates to the entire plate dropping a millimetre or so.

I decided to go ahead with this more or less as an experiment, and for my 5 x 4 metre building it worked, even with its 4 metre high pitched roof with galvanised steel sheet roofing (and a mezzanine floor for storage) - sterling board double skinned walls, except for the front wall which I infilled with herringbone brick under the windows.
The building has been up for six years now with no noticeable movement.

The only place that i have encountered a problem is with the supporting piers for the internal floor joists - it seems that the lack of water in the soil under the middle of the building has led to its drying out and shrinking - so my floor now has a graceful concavity towards the centre, that I am learning to love (until i get under and jack it up a bit).
This does raise questions about what to do with the water coming from the roof, the water butt that it fills is useful, but the authentic way of dealing with it for old rural buildings would have been to have overhanging eaves without gutters, so the soil got the water that it was familiar with, and therefore the building didn't become the cause of subsidence itself by drainage.

hope this is of interest.

 

[wytco0]

Hi David, that excellent information thanks for posting. Do you have any photos of your building that you could share either here or via email?

Thanks.

Tim