Slab foundation building in Portsmouth NH - a slab set up for New Hampshire winters
Building on a bare lot and need the slab right the first time? We plan the base, insulation and radon details before we pour.
- Fully licensed and insured.
- Free estimates at your property.
- We respond within 1 business day.
What does it take to build a slab foundation in Portsmouth?
The short answer: Slab foundation building in Portsmouth means pouring a concrete slab over a packed gravel layer. Heavy plastic sheeting or a vapor retarder usually goes on the gravel, and EPA radon guidance uses that layer to keep soil gases out of the house.
Most people who call about a slab are putting up a new house, an addition or a garage on a bare lot. The catch is that every choice under the concrete gets made before anyone can see it. The price mostly follows the size and shape of the footprint, how much digging and gravel the lot needs, and the insulation and radon layers you pick. The schedule turns on the city permit, any extra district review and the season, and we work all three into the plan before we set a pour date. Once I've walked your lot, the written estimate gives you the figure for your job.
How do you know it's time for a new slab foundation?
Plans but no foundation
You have drawings for a house, an addition or a garage, and the slab is the first thing that has to happen. If you decide the layers under it late, the pour can slide into cold weather and hold up everything built on top.
Old slab cracked and sinking
Cracks that keep widening, or a floor that has dropped in one spot, usually mean the base underneath settled. Patching the top won't reach that, and while you wait, water keeps working its way under the slab.
Water pooling by the walls
Puddles that sit against the building after rain usually mean the ground falls toward the house instead of away from it. Left alone, that water softens the ground the slab depends on, and it gets harder to fix.
How we handle slab foundation building
Once a slab is poured, whatever is under it is set for good, so before anything else I go over the edge insulation and radon details with you and your designer. In a cold climate like ours, federal guidance calls for insulation along the slab edge that meets or beats what code requires, so code sets the minimum and you can choose more. Then our crew digs out to the subgrade, the soil the whole slab rests on, and packs the gravel down instead of just raking it level, because a raked base settles with the dirt. I check where water runs on the lot so the ground falls away from the house. We set the forms, the edge insulation and the under-slab layers you and your designer settled on, then lay rebar, the steel that holds the slab together if it does crack. We pour early in the day so midday heat doesn't leave a weak, dusty top. After finishing, we cut control joints on time, shallow grooves that give cracks a place we chose, and let the slab cure, the wait while concrete gains strength, before anyone builds on it. If the budget gets tight, the base is the last thing I'd cut, because you can redo a floor finish later and you can't redo what's under a house.
Some lots and designs call for walls instead of a slab on grade, and that's foundation installation, which our crew does too. Property owners putting up a building that needs parking beside it can have us handle the concrete parking lot building as well, with the same care about the base and the runoff.
Slab poured in one piece
The thickened edges and the floor go in together, which suits a simple footprint on a fairly level lot. Fewer steps usually means a shorter stretch between digging and framing.
Slab inside foundation walls
The slab sits within separate footings or walls, which suits a sloped yard or a design that calls for more height at one end. It takes more work, but it handles ground that a one-piece slab can't.
What happens after you call about a slab foundation?
Here's how a slab job runs with us, from the first call to the cleanup, so you know who you'll talk to and what you'll have in hand before any concrete shows up.
- Step 01
Call or send a message
Call (603) 956-1034 or use the form, and we'll set up a time to see the lot. Have the lot address and any sketches or site plan handy.
- Step 02
I walk the lot with you
I come out myself, look at the slope and where the water runs, and ask how you'll use the building. Then you get a written estimate for your job.
- Step 03
Sort out the permit first
We work through any permit questions and get the papers together. The city lets work start only once the permit is issued, so we pick the pour date after that, with the season in mind.
- Step 04
Prep, pour, finish, clean up
Our crew preps the base, pours and finishes the slab, and cleans up the site. The slab then cures before framing starts on top of it.
Slab foundation building in Portsmouth: permits and districts
Portsmouth issues building permits through its Inspection Office, and new construction needs one, so a new slab goes through that office before we dig. If your lot sits in a Historic District zoning area, new construction or an addition also needs a separate Historic District Commission application, and the city says that adds at least an extra month to review. Lots in the city's Floodplain District, which covers FEMA flood hazard areas and the city's extended flood hazard areas, come with their own regulations. Check whether your lot falls in either district before you settle on a start date, and if it does, we plan around that review from the start.
We're based in Portsmouth and work in the cities around it on both sides of the Piscataqua, in New Hampshire and Maine. Tight side lots, sloped yards and the question of where the runoff goes come up on jobs in Rye and Kittery as often as they do here.
Get a written estimate for your slab foundation
We reply within one business day to set up a visit. I come out, walk your lot and send a free written estimate, with no obligation and no pressure to book.
Why Portsmouth homeowners call Portsmouth Concrete Works
Our own crew, me at pours
Our own crew does the work, and I'm on site for the pours. The person who planned your base is standing there when the concrete goes in.
Since 2017, awkward lots included
I started this business in 2017 after years on other crews learning flatwork and foundations, and we're known for sloped yards, tight side lots and old slabs that need opening up. I'd rather spend another hour puzzling out a tricky spot than leave a problem for you to find later.
Fully licensed and insured
We're fully licensed and insured. Ask me about it when I come out to look at the lot.
Historic and flood lots flagged early
On the first visit I ask whether your lot is in Portsmouth's Historic District or Floodplain District, because either one changes the paperwork and the pour date. Finding out early keeps a surprise review from landing in the middle of your schedule.
What matters most on a slab is what goes under it, and that starts with a walk around your lot. Get in touch and tell me what you're planning to build.
Slab foundation questions from Portsmouth homeowners
What do I need to apply for a building permit for a slab in Portsmouth?
You need plans or sketches that show the scope of the work, and most projects also need a site plan showing the lot, the structures on it, their sizes and the setbacks. Most residential projects don't need stamped structural plans, but the code official decides under state law when engineered plans are required, so it's worth asking early. We help pull together the sketches, site plans or drawings the office asks for.
How do I time a slab pour before winter in Portsmouth?
Work backward from the cold, because one builder's guide says the foundation should be done and the building closed in and heated before freezing weather. That means the permit and any district review need to be behind you with enough season left to frame and heat the house. Once the permit is in hand, I pick the pour date with that in mind.
Is a frost protected shallow foundation right for my lot?
It can be if your lot has a gentle slope, since one builder's guide says frost protected shallow foundations suit slab-on-grade homes on moderate to low sloping sites. On a suitable lot, that guide says the slab can go in with one pour, which speeds up construction. It's older national guidance, so we review it with your designer and the Inspection Department before counting on it.
Should my slab foundation include radon-resistant features?
It's worth deciding now, because the EPA says adding radon-resistant features during construction typically costs the builder less than fixing the home afterward. EPA guidance also says the sheeting on the gravel keeps the concrete from clogging the gravel layer during the pour. Settle the exact under-slab material with your designer, and we'll build to it.
How much does a slab foundation cost in Portsmouth NH?
There's no honest number until I've seen the lot, so your price comes in a written estimate after the site visit. A simple rectangle on a fairly level lot with easy truck access costs the least. A sloped yard that needs more fill, a tight side lot, an odd footprint or insulation above the code minimum all push it up.
What causes a slab floor to feel cold and damp along the outside walls?
Usually it's an edge that's losing heat, because where the coldest month averages below 45°F, the outer edge of a slab can stay below the dew point of the indoor air for long stretches, cold enough for moisture to form. That's the reason for the edge insulation we cover above, and it's far easier to get right before the pour than after.
Related concrete work for your new build
Foundation installation
If your design calls for full foundation walls instead of a slab on grade, this covers the walls and footings that carry the house above.
Concrete parking lot building
When a new building also needs room for cars, a poured lot built on a packed base handles daily traffic and sends water away from the entrance.
Talk through your slab foundation plans
Call (603) 956-1034 weekdays from 6 AM to 11 PM or weekends from 8 AM to 9 PM, or send the form whenever it suits you.