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Question DetailsAsked on 3/2/2017

cost of insulated shop with concrete floor. Shop 20 by 30. Also how much would it cost to add basement to shop

I am trying to figure how much I will need to add this to property in Idaho.

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Depends on size, soil conditions and normal code required depth of foundation for your frost zone, any shallow groundwater issues, etc. of course - but generally in the range of about $25-100/SF from cheapest and most expensive areas (not including any land cost of course). In most of country (yours included) generally I would expect bids from Builders - Garage/Barns/Sheds (your Search the List category for a contractor) to be in the $35-50/SF range - this for a garage/shop without any rooms above it - just garage-like structure with conventional attic.

Add basement to the plan - depending on your frost depth and groundwater situation, probably about $20/SF additional in deep foundation areas (where foundation has to be 3-4 feet deep anyway) to more like $30-40/SF additional if replacing an on-grade slab with a full basement (like maybe down near the Utah or southwestern Palouse area) or you have groundwater issues. THis assumes normall floor loadings - if this is going to have heavy equipment in it (more than a good sized pickup say) then of course the shop floor will need serious reinforcement so basement cost can go up $10-20/SF typically to be able to handle typical small contractor equipment - up to say an empty dumptruck or a D-6 dozer or such weight range say.

Bear in mind a 20x30 basement is before you put a stair in - you would be losing most of one normally short end wall about 3-1/2 feet wide for the stairs so becomes effectively becomes about a 20x26 space. So if that loss of square footage is important and you do not have high groundwater issues you might consider going with a staircase outside the basement footprint - not necessarily exterior, could be done as a doorway through the foundation wall and a cast concrete stairwell to above ground which lies outside the main foundation footprint as a bumpout for pretty minimal additional cost, then framed stairwell/entry on the outside of the shop building - which could also (at ground level) serve as an arctic/winter entrance to the at-grade shop.

Consider, for the basement, whether you also need access for large items - materials or power tools or finished goods like furniture if a woodshop for instance - you may want to put in a walk-down straight-in exterior stairwell or bulkhead door for that, or possibly a floor hatch in the shop to snake in or drop in large materials or equipment. I have done that scenario with a longish floor hatch (make sure it opens up right way for materials access from outside door) with special heavy duty shot-bolt fasteners below which actually dropped down rather than up to provide a ramp for sliding materials like lumber into the basement, and in another case by providing a built-in 2-ton chainfall hoist over the hatch to lower/raise shop equipment into a basement storage area. And of course frequency of access to the basement and your normal winter snow conditions will affect your access decision and needs also.

Of course, if you are going to build a boat in there or such, access needs changes significantly.

Don't forget for a shop use (both to keep materials dry and to minimize rusting of equipment) you want a dry floor without the normal soil moisture weepage through the concrete (which can total many gallons a day in wet soil conditions or rainy/breakup season), which is not as important in a garage - so unless on a high spot with excellent outside drainage you will probably want/need the slab to be elevated above ground level rather than at or slightly below ground level like a normal garage, and should have full vapor barrier installed under the concrete and the footer - commonly 6 mil but because of the foot traffic during concrete pouring I recommend 10-15 mil minimum - and of course rebar support has to be a non-penetrating blocking like bricks rather than wire chairs which would paerforate the heck out of the vapor barrier. This vapor barrier, combined with bitumastic sealant on the outside of the foundation wall, can essentially stop moisture migration from the soil into the shop/basement areas. This is particularly important in cases where the shop addition has its own heating, rather than sharing heating with the rest of the house which tends to absorb and distribute the moisture through the house. Also VERY important if the shop will normally run at lower temperatures, promoting condensation in surfaces in the addition.

To get a real budget estimate for your addition, I would start with an architect. You will need plans and specs to get a building permit and for bidders to bid to anyway, and for the successful bidder to build to anyway.

Or if considering a prefab building possibly a manufactured building vendor who can produce state-approveable plans using a local architect or structural engineer, though normally they do not do basements.

And don't forget if you want a bathroom out there, and your HVAC and lighting and power needs - especially if you will have a lot of power tools out there which might crank up power demand beyond what your existing breaker box can or reasonably should handle.

Also - pay attention to the floor finishes you want - for non-slip behavior but also for easy cleaning, and whether you want a hard finish like epoxy or urea or polyaspartic coating or just a sealer on the floor.

Also for cleaning - depending on whether vehicles/outdoor equipment will be coming in there, you might need floor slope and floor drain and drainage disposal facility, and if planning on hosing down the floor rather than just sweeping you might want the foundstion built with a wash curb - details like this are things an architect can help you consider, along with access issues, window or skylight lighting as well as good artificial lighting coverage, split-area lighting (so only the area you are working in is illuminated to save power), HVAC temperture setback provisions so it does not stay unnecessarily warm or cool if only sporadically used, etc. Also - architaect can commonly be very useful in getting building permit and any needed palnning and zoning approvals, which can be particularly difficult if this is going to be for commercial rather than hobby use.

Answered 3 years ago by LCD

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