Building a shed/workshop

[Joe K in Mississauga]

Hi All,

I'm about to build a large shed in my backyard that will function as a workshop as well. It will be approximately 14'x20'.

Here's my issue. The area I want to build it in is in the back corner of my yard and has some very large trees around it which have roots within a few inches of the surface. I originally wanted to pour a concrete slab and build the shed on that. However, with the roots, I'm afraid I won't be able to dig down deep enough for a thick enough pad.

Alternatively, I was thinking instead of building the base of the shed like a deck, by pouring several concrete pads/footings, using floor joists, and a plywood floor. The problem with this system is that it will raise the height of the shed by at least 12-14", accounting for the 2x8 joists and other hardware underneath the floor. I'm really hesitant to do this because I wanted the entrance to be within a few inches of ground level, and I don't want the structure to look too imposing.

Here then are my questions:

- What would you think is a better base for a shed/workshop that will have stationary tools like a table saw?

- I know the wood is more comfortable to stand on for long periods of time, but what would be better in the winter? Would the wood floor be colder because the cold air would circulate under the shed?

- If I was to pour a concrete pad, how thick should it be?

- If, let's say, the pad should be 8", can I pour it so that the pad is actually above ground, then gradually slope up 8" of earth around it.

- General thoughts/insights, past experiences?

I would be so grateful for any advice that can be offered. I want to get started by the first week of September, and need to finalize my course of action.

I know woodworking very well, but am a complet novice when it comes to concrete.

Thanks in advance.

joe

[Ken in Regina]

Good questions, Joe. I have no answer to whether the concrete of wood decking would be better in your situation, but a couple of small observations. The concrete won't be any warmer than an uninsulated wood deck. Concrete is not an insulator. You could insulate under either the concrete or the wood decking.

You would not need 8" thickness for a good concrete pad. If done properly (properly prepared base and quality concrete, properly poured) you should need no more than 4" or 5" at the most.

Yes, you could build the pad on grade or a litle bit above grade. You need to prepare the base for the concrete pad properly so there would still need to be some excavation.

The concern I would have about a concrete pad in this situation is the type of trees/roots that you would be covering with the pad. I would be concerned about whether their continued growth would create a potential for heaving the concrete pad.

[Ryan]

Joe,

I recently poured a concrete slab for a garden shed I built. I had a similar problem.

The way I poured my slab was to dig a trench 8 inches wide (width of a spade) and 10-12 inches deep around the entire perimeter. When I installed my forms I made sure that the top of the form was 4 inches above ground.

It's still a lot of work, especially with roots but what you end up with is a slab "keyed" into the ground at the edges and 4 inches thick. Then I just back filled some soil around the 4 inches that is higher than the yard.

I live in Whitby. if you'd like to see what I did, let me know.

[howard]

i don't know if any of this is of help but here are my thoughts and questions for what it is worth . . .

first thing to consider is the shed big enough, if you can possibly, given space and budget build it a little larger than you think you will need you are likely not to regret it and of course making a building a little larger does not usually substantially increase the cost

with regards to the large trees, you plan to cover part of their root system, is the rest of the root system uncovered or is it covered by other buildings, perhaps the neighbours or a paved alley etc. these trees need water and as long as you are not substantially covering their root system they should be fine, but if they are under a paved alley or a neighbours garage the area you cover might impact their water supply with disasterous results

having dug in soil with a good root system i would agree with you and avoid it, as well some trees do not do well with such disturbance and you may find that over the next five years or so they just die

personally i would build as you stated "like a deck" i have built several smaller buildings this way and been very happy, i would consider concrete posts that are poured into drilled holes, i would taper the holes, for example, using a smaller bore on the deeper part and a larger one on the upper, which is easy to do with any equipment such as a backhole or bobcat, this simple pointing of the concrete eliminates a large enough flat surface for frost to get underneath to lift the posts easily, i did this with a 18 by 22 foot addition attached to a second story and support by two posts only, it never shifted in the 5 plus years i was there after building it. i would not use precast deck posts because i think the size and the weight of the building warrants something other than a block resting on the ground.

yes you will raise the floor level a bit but depending how you reslope the yard and with the use of backfill it may not be as imposing as you fear, it also helps with any water issues you may have in the area, it also makes the building easier to move should you decide you want to do that in the future since the structure can be built independant of the footings and basically rest on them or be tied without too much effort by bolting.

your base for tools will be as good as its design, it would have to be very large equipment that generates a lot of vibration, in my opinion, to cause problems with a wodden floor properly built

wood is better in winter it does not transmit heat as does concrete and you can easily insulate between the joists as thick as you want, my one floor was R48 and even with a cold alberta winter wind was always comfortable and the room easily kept warm, i suppose that one could argue, perhaps someone will, contrary, but concrete insulated underneath still tranfers a tremendous amount of heat away from the room and though once heated can radiate some back in but it takes a lot of btu's to warm that slab.

another advantage of a wood floor is that you could easily install the ducting for your dust control system and floor electrical outlets etc. possible in concrete but much easier in a wood floor

just my two cents hope it is of some help

good luck

[Joe K in Mississauga]

Ken/Ryan/Howard,

Wow! Thanks a ton guys, for the rapid and well though out responses. This board is awesome, and I truly appreciate the time it takes to share your insights.

To clarify and respond to a few points raised by the three of you:

- I am stuck with 14'x20' due to the size of my yard and fact I don't want to build a visual wall that my neighbours have to look at. I know it's small but it beats the single car garage I have to work in now, which I have to share with, go figure....a car.

- The trees around the shed area will have lots of area to still soak up water. There are no other ground obstacles (eg. pavement) around the rest of the tree's roots.

- You've made me realize that pouring a pad is possible with the thickness you recommended and the fact I can keep it somewhat above grade. However I suppose the question now is, which do I want?

- The point about electrical and dust ducts under the floor is a very good point I really did not consider. Chalk one up for the floor.

- The point about the thermal properties of concrete is also intersting. Wood does sound more climate friendly in the winter, even with insulating under the concrete. Chalk another one up for wood floors.

- The root's ability to heave concrete in the future is also a consideration. One more for the wood!

So far the only real advantages to the concrete route are the fact I can build the shed slightly less high than the wood, and it would have a more permanent feel to it.

You guys have all given me a lot to chew on.

One more question before I finish this post. For those that have poured concrete, what was the rough cost? Was it a DIY project? My shed is unreachable by a cement truck since it's way in the backyard. I would probably need several people working with wheelbarrows between the truck and the pad, if I did it myself. I've heard that once the truck starts pouring it can't stop 'til it's done. How did you guys do it?

Thanks so much again, guys. You don't know how much I appreciate the advice.

joe

[howard]

pumper trucks can reach a long way back to deliver concrete at an added cost of course, if you talk to a concrete place they will tell you if they can reach your site. you are correct once a pour starts it continues until it is done, that would be a tremendous amount of concrete to move by wheelbarrow and remember while everyone, i would suspect at least five wheel barrowers, are deliverying someone has to be working the concrete on the other end

you also have to remove some of the topsoil in back and put in a proper gravel base and of course put all the rebar for reinforcement in before you pour, and by the way, the floor will have a crack or two guaranteed, - - that is what concrete does

good luck with your project and have fun

[howard]

oh and for a cost, why not call a couple of concrete places and ask how much for a one car garage pad, that will give you the best comparison, and for a DIY costs call a concrete company and tell them how many cubic yards you need of concrete (thickness times width times length) all in fractions of feet divided by 9 if my memory serves me, will give you cubic yards for concrete and gravel then call for a price for rebar and you should have your rough costs . . . i suspect from my experience that you will find it is more money and more labour

[Melvin in Calgary]

I'd go with the deck and piers. If you pour concrete over earth that has enough organic material in it to support tree roots your garanteed to get cracking and heaving. Not a good thing in a shop floor. Besides concrete is horrible to walk on; will be cold in the winter unless you put radient heat in the slab; and dropped objects will have a greater chance of breaking. Like other have said you also get greater flexability when running wiring and venting/dust collection.

Intended use and soil type will determine how many piers you'll need. If it's just you and normal wood working equipement regular live and dead loading alloances will be fine. Though you may want to place your larger equipement directly over a pier. If you intend to store wood inside you'll have to accomadate for the extra mass. If your getting a permit the inspector can help you with minimums. If any kind of flooding is possible a higher floor is better than something on grade.

How tall were you planning the walls? If overall height isn't a concern I'd go 10' at least. It's nice to have enough room for a 7' object on top of your assembly table.

Were you planning a large door or just a man size door? I'd have at least a set of double doors. A car size door could be handy but probably overkill. If price is a problem framing for the doors will only cost a few dollars and save a lot of work when you need to move that china cabinet out of your shop.

What style roof and are you using trusses or rafters? I'd consider a sissor type truss for the head room. If you were going to frame the roof a good solution is a clestory style roof running east-west with the windows facing south. Lots of light with minimal break in risk and some heat gain in the winter. (See end view in horrible ascii art below. Slope would be much less, like 4:12).

Think about theft risk when choosing windows and doors. Personally I would not put any windows facing my property line but esthetically that may not work for you depending on your site.

Put wiring in for lots of lighting on a couple different switches.

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[Felix in Brampton]

My shop, built 2 years ago is 13'10" x 18'6" (outside dimensions). This comes in just under the size (256 sq.ft?) for which the building code allows you to use a raft slab vs. a full depth footing.

Slab thickness at 3" is plenty, most slabs in industrial buildings are this thick. Save that concrete for more important things, like when you dig the deeper trench at the perimeter because that where the load bearing is required. Sawcuts at 6-8 feet are a good idea. Forget the rebar and ask for the fibre additive in the mix, does the equivalent job.

Get all the topsoil out. Rule of thumb is cutting one third of the roots is OK. Long term cut-off of moisture might be a bigger cause of concern; if you have downspots consider directing towards the trees.

If I remember correctly, I ordered 1.5 yds of concrete and that barely got got me there. Slab was 3" to 4" with a beefed up (10 to 12" deep) perimeter (it is hard to control to exact depth, a laser level to set the forms and get the stone at the right level is an excellent investment!).Concrete at that time was around $130 a yard with the fibre in.

[Jack in Nepean]

The previous posts are well thought out and I can add nothing from a construction perspective. I can, however, suggest that your feet, ankles, knees and hips will thank you for a floor with some flex to it (I'm just over 50 with knees just over 100). The down side is the possibility that moving large equipment (e.g. cabinet saw, 8" jointer, 15" planer) may be a bit more difficult. Larger wheels on the mobile bases would minimize that problem. FWIW

[Brent in Toronto]

Hi Joe,

Felix brings up the topic of building code which makes me wonder, have you looked into if this endevor requires a building permit.

It would be a pain to start building then have a building inspector arrive and tell you to tear it down.

In Toronto if a structure is to be permanent (ie poured foundation) and/or is over 100 sq feet you need a permit. Also structures have to be a certain distance from property lines and other structures. This amount varies by city.

Just a thought,
Brent

[J.P.Rap in Hamilton]

I can't add much to what was already said. The subject was pretty well covered. I was going to say pretty much what Brent said about size/ permit. I will add this though. A few years ago my brother looked into building a large shop on his property. He was restricted to the size allowed by the building codes. He later found out that by building with a post barn construction, the size codes did not apply. He was then only resrticted by the property lines. I susspect your codes are different then they are here in Hamilton. You had best check closley before making a final plan. Whatever you do, the building inspectors can be very helpfull in deciding the best way to proceed. You pay for them , use them.
It sounds like you leaning toward the wood floor. I have to admit, after reading this thread, I would be too. If you raise the grade for several feet in front of the shop before you start the slope, that would give you a smooth transition entering the shop. After a couple seasons of growth, it would look natural.

Good luck and let us know how you make out.
J.P.

[Rick in Calgary]

Howard, close but not right to figure out cubic yards you take the lenth x width x thickness and then divide by 27 if your are measuring in feet. Also it is a good idea which ever way you go to dig out all the black dirt and brown dirt all the way down to the clay. Then put a lift of clay and 4 inches of road gravel so it is the same level as the rest of the yard or alittle higher. Good luck on the shop!

[Rick in Calgary]

By the way most concrete is sold by the cubic meter not by the yard.

[Joe K in Mississauga]

Felix/Brent/JP,

Thanks for raising the issue of permits. I was thinking about that and was going to follow up with question on that topic.

Mississauga allows 108'sq without a permit. Based on my rough estimate right now, I like to build between 250 and 280'sq.

Because it's over the 108'sq, does this mean they have to go through the process of petitioning neighbours within a certain radius of my home to see if they have any problems with it? A neighbour 3 houses over added a second story a couple years ago and had go through a formal hearing - all neighbours within a 300' radius received notice from the city of the plans and were ivited to attend the hearing if they had objections.

OR, is there a certain size, above 108'sq, yet below another XX'sq where it's just a matter of having to pay a fee to the city and file formal plans?

I also have a worry about having an inspector over. When we bought the house 6 years ago, it had a sunroom addition (about 150'sq) that was not registered with the city. Obviously the owners that built it (2 owners before us) did not get a permit at the time. This addition has now been there for about 15-20 years. My worry is that the inspector will see this when he's over and make me tear it down. It's an important part of our living space now and I could not afford to rebuilt it if by chance they ordered it down. Can someone tell me how vigilant inspectors are regarding other things on the property if they come to inspect my shed?

Any opinions/advice would again be greatly appreciated. Anyone have any experience in particular with the city of Mississauga?

Thanks guys.

joe

[Joe K in Mississauga]

Melvin,

Thanks for the window idea. Kinda neat.

I especially like the slash key CAD drawing!

joe

[Felix in Brampton]

Joe;

You are permitted one accessory structure (not in front yard). If your setbacks and height are OK and you are not over a certain size (your size would be fine), you will not have to apply for a variance which means you would go to to committee of adjustment (the process you describe above).

I would think you'd be OK with the addition, unless you have to apply for a variance. If that's the case, all bets are off. If you already have an accessory building that you don't plan to tear down, that would likely also trigger variance.

[Norman (Metcalfe, Ont.)]

When we sold our last home I was surprised that our real estate agent asked to see the permit for the deck we built while we were there.

Fortunately, i had a permit registered.
This could be a new catch municiplaites are using to find out about any out-buildings, decks, sheds, additions, etc.. Wait till the property is for sale, then have the real estate agent do the footwork.

Norman

[Ken in Regina]

Joe, there are a number of criteria that will trigger a petition of your neighbors and it does not sound like you are likely to bump up against any of them.

Some of the things they want to know when you apply for a permit is whether the amount of your lot covered by buildings is greater than a certain percentage of the total lot size, the overall height of the structure, the height from grade to peak. And, of course, the structure needs to meet all of the relevant setbacks from the property lines and clearances from adjacent structures.

In Saskatchewan we also have to concern ourselves with underground utilities. We cannot put a permanent structure over the telephone, electrical or gas lines. If the utility lines are under the proposed space you need to take measures to mitigate that before a permit will be issued. For instance, the electrical company simply requires that you place a new duct under the pad so that if they ever need to run a new line they can simply pull a new cable through the spare duct.

However, that's not good enough for the phone company or the gas company. Both of them insist on relocating their services to where they will not be covered by the new structure before you can begin to build. Cost me $850 to relocate the electrical, phone and cable. I redesigned the structure's footprint and managed to miss the gas line by 2 feet or that would have been another $500.

[Franc]

Another thought for you regarding permits. We bought a different house three years ago and through the process got a little surprise. Around the same time as the bank assessed the property, our provincial assessors came around and discovered newer kitchen cabinets inside and a newer fairly large deck outside. Fortunately, it only increased our taxes with no mention of any retro taxes or payment of any outstanding permits. It just might pay to check out all the rules and follow them closely. Sooner or later, someone does find out about shortcuts.