Adapting Mike's Shed base to increase headroom, thoughts?

[g8dy]

Im 6ft4 and want to give myself as much headroom as possible in the shed so I stop hitting my head.

Raising the floor 150mm off my base would lose me too much. So I'm thinking of flipping a 100x65mm lintel on its shortest side and laying my floor joist on that. The floor would only be 65mm off my base. I know this is not ideal but having headspace is more important so have to sacrifice something I'm afraid.

I'll lay the joist headers (made from doubled up 4x2) directly on a mortar bed.

Question - There is no mortar between the Lintel and DPC right, it's just laid on top and let gravity do the rest?

 

[BucksDad]

It’ll be fine imo. When I took down my shed to build my workshop it was just sitting on some paving slabs, so only 5 cm off the ground and there wasn’t any rot - and it must have been there 10 years+ with the previous owner.

I believe the 150mm is also about rain bounce back onto wooden cladding etc. Well if you use plastic cladding throughout or at for the bottom 150mm you won’t have that issue.

 

[Spectric]

First thing I would change lookng at that drawing is to give the 50x100 more support than just a butt joint into the two 50x100 sitting on the sole plate. Why not use two lintels and give the cross members something to sit on. If you cannot do this and you go for the butt joint then drive some of these into the cross members to stop it splitting along the grain.

https://www.heco-schrauben.com/screws-accessories/screws/heco-topix-plus-combiconnect/
available from here

https://jandsfasteners.co.uk/heco-topix-cc-combi-connect-screws-t-drive/
As for the concerns over potential damp /rot then ensure that you remove any turf and have a shallow excavation under the shed filled with gravel, just a few inches ensures no damp soil.

 

[g8dy]

It’ll be fine imo. When I took down my shed to build my workshop it was just sitting on some paving slabs, so only 5 cm off the ground and there wasn’t any rot - and it must have been there 10 years+ with the previous owner.

I believe the 150mm is also about rain bounce back onto wooden cladding etc. Well if you use plastic cladding throughout or at for the bottom 150mm you won’t have that issue.

Agreed, a plastic bottom section is a good idea, thankyou!

First thing I would change lookng at that drawing is to give the 50x100 more support than just a butt joint into the two 50x100 sitting on the sole plate. Why not use two lintels and give the cross members something to sit on. If you cannot do this and you go for the butt joint then drive some of these into the cross members to stop it splitting along the grain.

https://www.heco-schrauben.com/screws-accessories/screws/heco-topix-plus-combiconnect/
available from here

https://jandsfasteners.co.uk/heco-topix-cc-combi-connect-screws-t-drive/
As for the concerns over potential damp /rot then ensure that you remove any turf and have a shallow excavation under the shed filled with gravel, just a few inches ensures no damp soil.

Thanks, i like the idea of an additional row of lintels but I'm dreading getting all these lintels level as I have part concrete base and part paving stones that these will be spanning across. All leveling will have to be done with shims, Ive never done any sort of mortar/shimming/brickwork before.

I was thinking instead of the extra lintels, using joist hangars like this -

Sabrefix Multi-Truss Hangers 50mm x 95mm 10 Pack - Screwfix

Could anyone confirm if the DPC just sits on the lintel and isn't fixed to the lintel in any way? Much appreciated.

 

[Spectric]

or something like these JHM100/50 100mm x 50mm Masonry Joist Hanger | Simpson Strong-Tie | London | Hertfordshire which secure from the top .

but I'm dreading getting all these lintels level as I have part concrete base and part paving stones

So why the two beds of mortar, if you bed the lintels down on a strong mix and get level then all you need to do is lay a DPM on the lintels and then your timber, cannot see why this needs a bed if you get the lintels level. On mine I used a heavy duty rubber mat cut into strips for the DPM as it allowed more give.

When it comes to fixingthe metalwork to the timber use something like these Heco Topix Flange Head T40 A2 8.0 x 80mm

and bitumen the ends of the timber to prevent water engress.

 

[Fitzroy]

Mike's way is the gold standard and a great start point, you need to consider what each element of the design achieves and then decide if you are concerned about removing it. If I were building a 50+ year workshop and spending 10k+ I'd want to follow it 99%+. However, my build was move like 2k (when materials were reasonable) and so I stepped away from many element of Mike's design.

Looking at your proposal vs Mike's
- Your DPC will only protect you from moisture entering the timber from below, any splashing could penetrate your joist headers and migrate to your floor joists. Mike's brick course with over wrapped DPC is aimed to prevent this.
- Your design does not have any underfloor ventilation, Mike's does which will allow any moisture that get's past his brick course to evaporate later.
- Mike's brick course are taller than 30cm which is the limit of splashing from rain, with good overhangs and gutters this keeps the majority of rain off of the building, reducing the weathering of the structure.

I was going to suggest joist hangers to enable you to minimise the underfloor void depth, additionally your drawing indicates 100mm deep floor joists. This depth of joist will not span much width without sagging under load, using some intermediate supports may be required. An appropriate height block mortared in place with a piece of dpm on the surface would suffice.

I would think about how you can introduce some ventilation under the floor, to mitigate any moisture build up.

Extending your external cladding/weather screen past the joist headers will prevent them getting wet and transferring moisture. I'd extend it as close to the floor as possible, knowing the cladding may suffer over time but that's easy to maintain/fix.

Yes the DPM just sits in place with no fixing.

Fitz

 

[Spectric]

But do not forget it is a shed at the end of the day and not a building for habitation, overkill cost money without huge benefits.

You have shown just a single point of your intended plan, can you give an overview of total layout as if the span is to great then as Fitzroy has said the 100mm timber will sag, and extra support will be required.

 

[g8dy]

or something like these JHM100/50 100mm x 50mm Masonry Joist Hanger | Simpson Strong-Tie | London | Hertfordshire which secure from the top .


So why the two beds of mortar, if you bed the lintels down on a strong mix and get level then all you need to do is lay a DPM on the lintels and then your timber, cannot see why this needs a bed if you get the lintels level. On mine I used a heavy duty rubber mat cut into strips for the DPM as it allowed more give.

When it comes to fixingthe metalwork to the timber use something like these Heco Topix Flange Head T40 A2 8.0 x 80mm

and bitumen the ends of the timber to prevent water engress.

Yes thats perfect thankyou! For the hangars that secure from the top, would I need to somehow fill the small gap that the thickness of the hanger will raise the bottom plate of the wall by? Or is it negligible?

Mike's way is the gold standard and a great start point, you need to consider what each element of the design achieves and then decide if you are concerned about removing it. If I were building a 50+ year workshop and spending 10k+ I'd want to follow it 99%+. However, my build was move like 2k (when materials were reasonable) and so I stepped away from many element of Mike's design.

Looking at your proposal vs Mike's
- Your DPC will only protect you from moisture entering the timber from below, any splashing could penetrate your joist headers and migrate to your floor joists. Mike's brick course with over wrapped DPC is aimed to prevent this.
- Your design does not have any underfloor ventilation, Mike's does which will allow any moisture that get's past his brick course to evaporate later.
- Mike's brick course are taller than 30cm which is the limit of splashing from rain, with good overhangs and gutters this keeps the majority of rain off of the building, reducing the weathering of the structure.

I was going to suggest joist hangers to enable you to minimise the underfloor void depth, additionally your drawing indicates 100mm deep floor joists. This depth of joist will not span much width without sagging under load, using some intermediate supports may be required. An appropriate height block mortared in place with a piece of dpm on the surface would suffice.

I would think about how you can introduce some ventilation under the floor, to mitigate any moisture build up.

Extending your external cladding/weather screen past the joist headers will prevent them getting wet and transferring moisture. I'd extend it as close to the floor as possible, knowing the cladding may suffer over time but that's easy to maintain/fix.

Yes the DPM just sits in place with no fixing.

Fitz

Hi Fitz, thanks for this info, much appreciated, to answer your points (with a sketch too)

- Ill be going down to ground level with the external cladding to protect from splashes, I guess it will be sacrificial, will treat all sawn ends too.
- Ill be laying the lintels only in rows (like normal shed bearers) and not creating a sealed rectangle so the ends will be open for ventilation, Ill put down insect netting all round to keep out rodents, but I'm not too bothered about rats as I have 3 neighbours cats who all hang out at the back on my garden.
- Will install guttering to try and reduce splashing

According to span tables. C24 44x95 placed 400mm can span approx 1.5m. Ill be placing lintels 1m apart. It should be sufficient I think.

 

[Sachakins]

It's less about the gap off the floor and more about the air flow under it.
Sheds/workshops pushed tight into a corner against a fence often tend to rot in the corner that's tight into the fence corner.
Siting it 300mm in from each fence will reduce this occurance, siting in 600mm even better, as you can around the shed/workshop to do regular maintenance.

These gaps allow for more airflow, which reduces damp and vermin, as airbag exposes the space and forming don't like on spa es.