Radon Mitigation in Londonderry, NH

A radon mitigation system gives the gas a way out of your house that is not through your living space. Pipe, fan, sealed entry points, and a way to confirm it is working. If you have a test result in hand and you are in Londonderry, we can look at it.

What radon actually is, without the scare

Radon is a gas that comes up out of the ground and gets into houses through the lowest level. You cannot smell it or see it. At high enough levels over long enough it is genuinely bad for you, which is why testing exists.

The reason we lead with testing rather than selling: your neighbour’s number is not your number. Houses fifty feet apart test differently. Get your own.

How the system works

The common approach is sub-slab depressurization. We core the slab, put a pipe into the material under it, run that pipe out and up, and put a fan on it. The fan pulls a slight vacuum under the slab so the gas goes up the pipe instead of into the basement. Then we seal the obvious entry points, the floor wall joint and any open sump, so the system is pulling from under the slab and not from your basement air.

Crawl spaces work a bit differently. The membrane becomes part of the system and we draw from underneath it.

Testing before and after

We test, we install, we test again. That second test is the whole point, and you should insist on it from anyone you hire.

603 holds a state radon measurement certification, RMS-113966.

What we will not promise you

We will not guarantee a specific radon number unless we put that number in writing for your house.

Plenty of outfits will promise you a level over the phone. We would rather test your house, install the system, test again, and show you where it actually landed. If a specific result matters to you, and for a real estate closing it usually does, get it in writing before the work starts. From us or from anybody else.

The warranty

Radon mitigation carries a 10 year warranty on system integrity and components. That covers the system. It is not a guarantee of a radon level, for the reason above.

Questions we get

My house is new. Do I still need to test?
Yes. Construction age does not tell you what is under the slab.

Is the fan loud?
You should hear a low hum at most. If a system is noisy or rattling, something is wrong with it and it is worth a call.

Does it run all the time?
Yes, continuously. Turning it off means it is not doing anything.

What about radon in water?
That is a separate test and a separate system from the air side. If you are on a private well it is worth asking about.

I am selling. How fast can this happen?
Tell us the closing date when you call. Most installs are a day.

Reading your test result

Situation	What it means	What happens next
Short-term test came back high	A snapshot, and worth acting on	Confirm, then look at the house for a system layout
Two tests disagree	Normal. Radon moves with weather and season	Longer test, or treat the higher reading as the planning number
Buyer or seller needs a number	There is a deadline attached	Tell us the closing date when you call
Finished basement, no test yet	People spend hours in that room	Test before you spend anything else on the space
Crawl space rather than a slab	Different system design	The membrane becomes part of the system
On a private well	Water is a separate pathway from air	Separate test, separate system if needed

How the job runs

It starts with a number. If you already have a test result, bring it. If you do not, that is where we begin, because there is no sense designing a system for a house nobody has measured.

Then somebody looks at the house. Where the slab is, where the pipe can run, where the fan can sit so you are not listening to it in the room above. That layout is most of the job and it is why we do not quote it over the phone.

On install day the slab gets cored, the pipe goes in and runs out and up, the fan goes on it, and the obvious entry points get sealed so the system is pulling from under the slab rather than out of your basement.

Then we test again. That second test is the point of the whole exercise, and you should insist on it from anybody you hire, us included.

What is actually under Londonderry

Londonderry sits across four USGS quadrangles, all New Hampshire: Derry, Manchester South, Nashua North and Windham. Published surficial maps exist for all four. Bedrock is a thinner record, with a 1:24,000 map published only for Windham.

Four bedrock units underlie the town, including the Berwick Formation of the Merrimack Group and the Massabesic Gneiss Complex. The USGS notes that the well-bedded Berwick is exposed in roadcuts near the interstate in Londonderry, which is to say you can see it on the drive.

Drainage, by the numbers

Of the town’s mapped soils, about 56 percent are well drained and 11 percent excessively drained. But 12 percent are very poorly drained and another 3 percent poorly drained, so roughly one acre in seven is ground that holds water. The town’s own plan reports 52 percent of its soils in Hydrologic Soil Group B and about 22 percent in Group C.

The restrictive layers are the detail that matters for a foundation. Hollis soils record lithic bedrock at a representative depth of about 38 to 41 centimetres, Chatfield at about 76, with rock outcrop at zero. Where compact till is the restriction, water moving down stops there and moves sideways instead.

Shallow bedrock and dense till do the same thing to water. They send it somewhere else, and somewhere else is often the nearest foundation.

Where the town is dry, and where it is not

Over 93 percent of Londonderry is FEMA Zone X, which is minimal flood risk. The higher-risk ground is specific: upstream of the Little Cohas Brook Reservoir, upstream of Kendall Pond, near the Beaver Brook headwaters. Wetlands cover about 2,501 acres, roughly 7 percent.

The town is 72 percent bedrock aquifer and 24 percent stratified drift. Impervious cover is 10.3 percent, just over the 10 percent mark at which stream quality is generally considered impacted.

Being in Zone X does not mean a basement stays dry. Most of the wet basements we see have nothing to do with a river and everything to do with water in the soil beside the wall. That is a different problem with a different fix, and it is what the inspection is for.

Aquifers, wetlands and the shape of the town

Londonderry has four major stratified drift aquifers, and the town’s plan places them primarily near the municipal borders. The bedrock is recorded by the town as 82 percent metamorphic and 18 percent plutonic igneous, with the plutonic ground concentrated in the northwest corner.

Wetlands run to roughly 2,501 acres, about 7 percent, and about 60 percent of that is freshwater forested and shrub rather than open marsh. Forested wetland is easy to miss from a driveway and it is still wetland.

The town is drained east by Beaver, Indian and Black Brooks, and west by Little Cohas Brook and its neighbours, all within the Lower Merrimack River Basin. Three of its watersheds already carry impervious cover above the 10 percent mark.

What our customers say

Branden came out to the house, listened to my concerns, and talked to me about the possible solutions for my basement waterproofing and radon system. I accepted the more extensive proposal and within six weeks (which was perfect for me) the work was being done. The team that performed the work was very professional and hardworking. They were able to complete the basement in two days. I’m very happy with the results.

Karen Howard, Google review, 5 stars

That is one of more than 240 Google reviews. We would rather you read them than take our word for anything on this page.

Related pages for Londonderry

Book a free inspection in Londonderry

Somebody comes out, looks at the actual space, and tells you straight what it needs and what it does not. You get a written number for a defined scope. No two hour pitch, because we would rather be at the next house.

If you are looking for a team that isn’t going to treat you like another number, we would be happy to give you an estimate free of charge. We don’t cut corners. We stand behind our work. We care.

Call 603-610-1770 or book your free inspection. We cover Londonderry and the surrounding towns from our shop in East Kingston, New Hampshire.

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