Foundation depths and DPC

[wjm]

Hello all,

I need some advice. I am about to build a concrete block shed in the garden. (Don't need planning permission in my area thank goodness!). It will most probably have some kind of felt roofing. I'll be using normal concrete blocks (440x215x100mm) the query I have is how deep should the foundations be. The ground type is muddy clay (!) as you start to go down. I've read somewhere the width of the foundation strip should be double the width of the block (i.e 200 mm), but the depth eludes me .

Another quick question. I'll be putting down the damp proofing sheeting under the concrete floor in the shed, is it normal to fold this sheeting up at the edges and use as the dam proofing course for the blocks or should a separate dpc be used for the blocks?

Any thoughts / answers ( ) gratefully received.

 

[masona]

This is a difficult one,all depends what you want the shed for.Most people just build a 6" concrete base with membrane underneath + approx 12" footing round the edge to take the weight of the walls then use engineer bricks on top of the base to DPC level (150mm at base level) then your celcon blocks on top of dpc + the walls will have to be rendered.Do not use celcon blocks straight on top of footing -you will have damp problems.

OR you can have a footing with common or engineer bricks on top to dpc level,oversite fill in with reject or hardcore then pit sand + membrane 150mm below dpc level and slide it under the dpc with 100mm concrete + 50mm floor screed.This is really for extension building etc.Like I say depend what you want the shed for and how fussy you are.

Sometimes we can go over the top for unnecessary work but the choice is yours.

Have a look at this website to help you or I can help you as you go along.

 

[masona]

(Don't need planning permission in my area thank goodness!).

Forgot to add,if you don't need planning permission then you will need building permission which is straight forward.You can get the details from your local planning handbook guide for householders. e.g in our area the shed/workshop must be 5m away from the property and flat roof must not be higher than 3m or pitch roof no higher than 4m and doesn't take up more than 50% of your garden. I thought I mention it as your neighbours could disapprove, but not if it within the guideline of the building control.

 

[wjm]

Thanks for the info masona,

The regulations in our area are the same except instead of 50% it has to be no larger than 30m2.

The shed will be kind of an office/gym/(shed), so I want to make sure it is a good standard.

In the picture above, if I am using a dpm sheeting (such as this) and it it tucked into the first layer, does this act as the damp course or should a dpc be used as well?

(In the diagram I wrote DPC sheeting but is of course DPM sheeting)

Also in this situation can concrete blocks be used as the first layer as it will be outside the DPC and DPM , so in thoery any damp should be stopped.

Thanks for the help by the way- much appreciated

 

[masona]

does this act as the damp course or should a dpc be used as well?

No it won't,so use a dpc (see this ) on top of your dpm sheet as well.The dpm sheet won't be flat & you will get ripple effect on top of the wall all the way round,so dpc will be flatter,stronger and easier to bricklay as with dpm sheet, the cement + cement blocks will keep sliding off the sheet.I would use 3 courses of engineer brick (not much dearer than common brick) which will give you approx 150mm high to dpc level which is waterproof and frostproof.Then a layer of cement under the dpm sheet on top of the wall with dpc on top then cement again with blocks etc.Also make sure the return wall on the externel corner is minimum 450mm when fixing door/window frame.

 

[wjm]

Thanks for your help, that's what I'll do.

 

[MrRegs]

you will need to be carefull if you are building a building that will be used for any thing other than what is the norm is for say a shed (check B Regs for detail) you may find that B Regs applies and all standards of construction relating to say an office will apply. Similarly the planning TP Acts may require permission

 

[masona]

Good point,just read the 'B' Section regarding office,

The building or structure is not to be used for purposes ancillary to domestic use and is to be used instead,for example,for parking a commercial vehicle,running a business or for storing goods in connection with a business.

But this is in my area not sure if it the same elsewhere.

 

[MrRegs]

for an explaination of what is exempt from the Regs then youll need to refer to schedule three "Exempt building and structures".

However there is no reason to prevent a shed being built to a standard that enables you to use as an office. You should bear in mind that you will not be able to sell the property as an office

 

[skellem]

This might make it easier, slightly more detailed because I know how you can scratch your head when it comes to building it! I've been there!

Ignore the foundation sizes, this was for a garage that I drew up for someone, so they may not apply to you.

 

[wjm]

Thanks a lot people, that's very helpful.

Cheers

 

[breezer]

Skellem, that drawing, what prog did you use to do that please?

 

[masona]

The way you produce an image like that is to load up MSPaint, located at;
Start > Programs > Accessories > Paint. To upload it to here, you'd have to compress it to a .gif / .jpg and then upload it to a webserver. Theres a couple of free ones.. geocities.com, angelfire.com to name a few. Then you just simply use the tags to insert it into your post.

Impressed, yeah? :)

 

[breezer]

i thought it looked too good to have been done in MS paint

 

[masona]

I'm guessing skellem done it that way because it does look like MS Paint to me.

Unless skellem proves me wrong