Wooden Workshop Base

[James C]

After years of waiting I should soon hopefully be in a position to construct myself a workspace at the bottom of my garden.
My plan is to assemble a 40mm thick log cabin which can be viewed on the link below.

https://www.tuin.co.uk/Aiste-Log-Cabin-5-x-3m.html

To try and keep costs down, and so that I have completed some of the construction myself, I am planning to construct a wooden base for this using 6x2s bolted down to 4x4 posts would be fixed in 12x12 holes with postcrete or a similar product.
The plan is to make a base that in total is 16x12 for a 16x10 log cabin. I would then deck the 2' of base in front.

https://ibb.co/0YYCpZW

This is looking sideways on with the longest span running away. On the right you can see where the decking would be supported with two joists. The main joists that are not attached to the posts are currently at 350mm centres. I have yet to add any noggins to this design, as I want to get the joist spacings correct first.

Bearing in mind that I plan on adding a large workbench, 140Kg Bandsaw, 85KG Morticer as my heaviest items of machinery, do I need to have narrower centres for my joists? Should I add an extra row of 5 posts?

Any help and guidance would be appreciated.

 

[HappyHacker]

James,
I cannot comment on the structural elements of you design but after many years experience of sticking bits of wood into concrete I would make the following recommendation:

Do not put the vertical ground posts into the ground (concrete), even with careful detailing of the concrete around the post and using treated posts you will get a maximum of 20 possibly 30 years and probably much less before they rot. Instead use something like https://www.toolstation.com/post-base/p29420 stick with the galvanised options, the painted ones last no time.

I have just replaced a 6" square treated post that was completely rotten below ground, it had been in about 25 years, I replaced it with a 8" post on the basis that if it lasts another 25 years I will not be here to worry about it. One nearby failed about 5 years ago. I recently took out some 4" posts that had been in about 15 years on a fence, some were solid others were rotted through, all in concrete.

If the floor joists do not have to be very high of the ground use one of the many decking joist supports that will keep the joists a few inches off the floor and usually allow some element of adjustment so your concrete pads do not have to be spot on.
Kevin

 

[MikeG.]

Concreting posts into the ground is a guarantee of failure. There are lots of better ways. Be aware that any suspended floor on posts leads to an unsealable void below the floor (which rats love), and to a large step up into the building.

You might be able to adapt the base detail from the second link in my signature, below, to use with your off-the-shelf shed.

 

[James C]

Thanks both for your suggestions. The more and more I read, the better off it seems I would be using a concrete slab.

I think that I will bite the bullet and when the time comes get some quotes for someone to come and lay a slab for me.

 

[MikeG.]

It doesn't stop at a slab, I'm afraid. You must raise the base of the timber shed off the ground on a brick (or block) plinth, a minimum of 150 high.

 

[James C]

It doesn't stop at a slab, I'm afraid. You must raise the base of the timber shed off the ground on a brick (or block) plinth, a minimum of 150 high.

Mike I have properly read through your Building a Shed without concrete thread and it was very helpful. I am now on WH2 reading Michaels build.

 

[RobinBHM]

Im building a garden cabin / office.

Due to narrow access, I decided against a slab. I dug out 3 trenches, whacked in some pegs, then screwed on shuttering -set plumb with a laser level. I then used these as sleepers and laid the 5 x 2 joists on top.

It is compromise due to the risk of rats like Mike stated.

So far its fine, the 5 x 2 joisting is plenty solid enough as the span between the concrete strips is about 1200mm. I laid strips of upvc trim 40 x 10 so the timber isnt on the concrete.

I also have a shed, which I dug out for concrete pads, laid these level, then put on some universal beams and ran the joists on the top. the rear of the shed is almost next to a small brook, so I dug some of the pads down 1600mm .....

 

[James C]

Thanks all.

I have had a play around with the layout of some Concrete Lintels looking at the sizes of my closest supplier, Travis Perkins. They seem to use sizes of 965mm, 1830mm and 2440mm. With this in mind I could arrange them into a base that would be 4825mm x 2795mm which I think would suit my off the shelf shed planned purchase which is 4800x2800.

https://ibb.co/2Fdhc0x

I'm not too worried if between 0-5mm of one 40mm log wall is overhanging the base.

However, I understand the importance now of raising the shed above ground height to avoid splashback as well as sitting in water.
If I have a strip of the base exposed on each side of around 1/2" will I need to worry about splashing and rotting on my shed, or is such a small strip neglible?

 

[MikeG.]

Best avoided if you can help it, James. Try to avoid ledges on which water can sit. The idea is that there is a clear path for rain water to run to ground, without any possibility of pooling anywhere. Those lintels are cut relatively easily with a 9" angle grinder.

 

[woodbloke66]

To try and keep costs down, and so that I have completed some of the construction myself, I am planning to construct a wooden base for this using 6x2s bolted down to 4x4 posts would be fixed in 12x12 holes with postcrete or a similar product.
The plan is to make a base that in total is 16x12 for a 16x10 log cabin. I would then deck the 2' of base in front.

The base of my 'shop uses lots of very heavy, 50mm thick concrete paving slabs arranged in a series of piers, onto which goes proper 'old skool' creosoted, genuine railway sleepers laid on their edge; the 'shop is built on top - Rob

 

[James C]

Best avoided if you can help it, James. Try to avoid ledges on which water can sit. The idea is that there is a clear path for rain water to run to ground, without any possibility of pooling anywhere. Those lintels are cut relatively easily with a 9" angle grinder.

That's good to know. I think working with shorter lengths will be easier, and using multiple lengths cut to size will be cheaper as I can buy in bulk of 10+.

Thanks

 

[James C]

I am happy with the layout and use of Lintels, so now comes my next question. :roll:

Most of the Periscope Vent I can find when used upside down have an aperture of 200mm x 50mm. Pretty much all of the timber I have been able to check so far near me has FIN dimensions of 95mm x 45mm.

Can I bed the vent down into the mortar under the sole plate so it sits flush with the sole plate? This would mean having 10mm of mortar under the sole plate and 5mm under the vent. I have mocked this up in Sketchup in case my explanation doesn't make sense.

https://ibb.co/hLTP1h0

Many Thanks

 

[MikeG.]

Yes is the answer. Bed the plate on mortar.