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Community and Q&A

Insulation and venting for a well pump house

MStaudaher | Posted in General Questions on

I have a well on my property that I need to build a well house for to protect the pump equipment/plumbing and to prevent freezing in winter.  The well house with the equipment will be about 20′ from the actual well head.  The development my property is in allows for a well house structure to be a maximum of 8’x10′ in size.

My question is how best to insulate the building to prevent possible freeze damage to the pump equipment in the winter (climate zone 5B)?  The exterior cladding will be fiber cement siding and the roof will have architectural shingles to match my residence.  Can I insulate the walls and rafter bays without any vents in the building or do I need to insulate the ceiling below the roof and have a ventilated roof?

Also, the building will be on a small 8’x10′ slab.  Should I use rigid foam insulation under the slab and/or around the perimeter of the slab?

I have been told by a local well driller to install a small cadet heater in the building set for about 50 degrees to prevent winter freezing.  Does anyone have any suggestions?

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  1. Expert Member
    BILL WICHERS | | #1

    Since this is just an equipment shed, and not an occupied structure, I doubt anyone will try to hold you to residential building codes regarding insulation. I would insulate the building in a fast and easy way. Assuming you’re framing the walls with 2x4 (or 2x something, it doesn’t really matter for insulation ideas), I’d put 2” polyiso over the outside of the walls, siding over that, and structural sheathing on the interior wall. I wouldn’t bother filling the wall cavities, but you could if you wanted a bit of extra insulation. This is a bit backwards compared to a regular wall and here’s why: you’re going to want strong interior wall surfaces so that you can easily mount equipment to them (filters, shelving for parts, etc). You don’t need drywall, so plywood is better. With plywood walls inside, you don’t need exterior structural sheathing, so you can put rigid foam directly on the studs without worry about racking issues. Hang your siding on furring strips over the rigid foam in the usual way.

    For the roof, I’d try to put rigid foam on top, for the same basic reason (it’s an easier surface to work with). I wouldn’t try to vent the roof, and with the underside of the sheathing open to the room, you shouldn’t have issues since air can circulate inside the shed.

    If you only have electricity available for heat, I’d use a small electric “garage heater”. There are lots of options for these. I’m not sure if you can get one under about 3kw, but I’d be tempted to use a 5kw unit anyway just to have some extra margin. Run heavy enough power cable to the shed to run a small subpanel, and use that subpanel to power everything — the heater, the well pump, lights, some receptacles. I’d strongly recommend running the power cable using THHN wire (or equivalent) inside PVC conduit and not using UF cable directly buried.

    I’d run a second PVC conduit for control wires. Put a small/cheap MECHANICAL heating-only thermostat inside the shed, and run a two wire loop from that thermostat back to your house. In your house, connect a small transformer and a bell. Set the thermostat maybe 2 degrees under whatever temperature you want to keep the shed at. You now have an undertemperature alarm that will alert you to a heater failure in the shed and possibly protect you from some major repair expand some day. By powering the alarm from the house, it will still work in case the heater on the shed fails due a power problem in the shed. I’ve used this same setup many times in greenhouses to warn against nighttime heating problems.


  2. Expert Member
    Peter Yost | | #2

    HI MS -

    Since heat loss is always a combination of conduction (insulation) and convection (air sealing) make your building as airtight as you can as you insulate it.


  3. MStaudaher | | #3

    Thank you for the replies. There is no permitting needed for structures this small in the county where I live. I was concerned about the venting needs for such a structure. It would be a lot easier to insulate and air seal if I didn't have to deal with the need to vent the roof in such a small building.

  4. MStaudaher | | #4

    Any thoughts on my question about the need for sub-slab and/or perimeter slab insulation?

  5. Expert Member
    BILL WICHERS | | #5

    I would build the roof unvented, and not build a ceiling (leave the roof assembly open inside). Air seal the roof/wall connection. You do need good air sealing as Peter points out. You don’t need extra ventilation in this since it’s a small unoccupied structure.

    I would not bother with subslab insulation, but that’s just me. You could insulate under the slab and around the perimeter, and that will save you a bit on heating costs. If you’ll be excavating at the site anyway, then the foam probably makes sense. If you’re really just pouring a slab in a form on top of the ground, then I wouldn’t use any foam underneath. You could put foam on top of the slab and use a subfloor in a slab on grade, but you’re building a pump house — stuff is going to leak occasionally. A wooden subfloor in a mechanical building where leaks are a real possibility, and those leaks might not get noticed for a while, is asking for trouble. I would put poly under the slab.

    I’d also put a floor drain in and drain it to a small drywall nearby. Just in case something leaks. I maintain 5 water wells for family and I can tell you, something will always leak even if only when you’re working on the system.


  6. user-6185887 | | #6

    I say smaller the building the better, less surface area = less energy loss.

    Build it to look like dog house that you can lift the roof off for service.

    I do not think underground insulation is worth the effort as you set point is likely to be close to 40° so you have a small differential.


  7. Jon_R | | #7

    There is no way to use a submersible pump and avoid the well house completely?

    In this case, the ground is a heat source - better not to insulate it from the pump house. But you do want exterior wings of underground foam to keep outside cold from getting under the slab (see frost protected shallow foundations for drawings).

    Do use plastic sheet under the slab to prevent moisture in the building. No moisture means no need for Winter venting.

    You could heat this building with just the well water (but tricky since you need assured flow).

  8. Expert Member
    Peter Engle | | #8

    You should also consider humidity issues in summertime. With a sealed building, cold well water and a few inevitable air and water leaks, you're going to get condensation on the well pipes, tanks and equipment. You will probably need to dehumidify the air in summer to keep the interior from getting moldy and to limit corrosion.

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