Crawlspace Required?

My builder has said we will be doing a crawlspace underneath the 8' x 8' mudroom that will connect my new garage to my existing home. With that, he has said it will need a radon pump, drain tile, 2'x3' access door, ventilation, and vapor barrier. All of this work and $$$ for a tiny, seemingly unnecessary crawlspace seems ludicrous. Can't we just fill the area in with soil/gravel, or is this against code since there will be a wooden structure (floor joists) above? If a crawlspace is required, then I think I'm going to condsider doing a stilt construction. Although he seems to think the floor will be "freezing cold" if I go that route (isn't that what insulation is for?).

 

How thick will the fill need to be? Have you discussed that option with the builder?

Generally a concrete floor is colder than an insulated wood floor. A floor that isn't underpinned can get cold, even with insulation. Probably best to go with spray foam if you go that route.

 

Not sure what you mean about how thick the fill needs to be.

 

Also, when he says "ventilation", he means I need a supply and a return vent in the crawlspace and a heat load done by a contractor. Wth? It's going to be an unlivable livable space with it's own door. I might as well add a light fixture and a plug and rent it out

 

Never once heard of anyone having to use a radon pump in VA, what makes him think it's needed?
I agree 100% with a full foundation, drain tile and vapor barrier on the ground.
Looked at any of the hundreds of other post on this and any DIY site about people having moisture issues under there homes?
Have them install the auto opening vents not the manual aluminum one's.

 

You have two options; the crawl space or fill and compact and have a concrete slab.

The crawl space is likely the cheapest option. And a crawl space is a crawl space. There must be access, ventilation and vapor protection. You also likely have to maintain a minimum height of 24". These are all very normal requirements for a crawl space. In the future when you want to run a new electrical outlet or cable for TV you'll appreciate it.

You can also fill the space and pour concrete. You will have to either back fill the space with crushed stone or with soil that is properly compacted. If you go with soil they will likely want an engineer to sign off on the compaction which is often not required when using stone. Then on top you'll have a vapor barrier, insulation and pour your concrete.

Piers is not a good option. It would be if you were in the mountains on a steep slope but not in flat lands. If you go piers you would have to totally sheet and enclose the bottom of the floor to protect the wiring and insulation which adds to the cost. Then you're stuck with an odd low space under your building that attracts critters and is aesthetically odd.

 

This mudroom is simply to connect the garage to the dining room and I don't foresee having to run anything ever, but who knows. Good point.

There won't be much backfilling required as the area is only about 12" above grade. I think I like this option the best. However, is it okay to put floor joists on top of a slab? My builder seems to think this is against code, but I can't imagine why it would be.

All good points, and this is the least desirable option.

 

Oh yeah, it's pretty common around here. I have several neighbor's with pumps.

Foundation, drain tile, and vapor barrier...that's fine. But my builder is saying I need a return vent and supply vent in the crawlspace to condition it. That seems ludicrous. Wouldn't a single foundation vent to the outside suffice/be to code?

 

Unless you are going to have ductwork or plumbing underneath and need the access, I don't know why this addition wouldn't just be an insulated concrete slab on a foundation, like Pilot Dane mentioned. You could even add radiant heat to the floor if you wanted. Much better use of $$$.

 

In case it went unnoticed...

Is it okay to have wooden joists on top of a concrete slab? This would be ideal as I could insulate the joist cavities and run my HVAC duct in a cavity as well.

 

That would be quite unusual. Ductwork can be insulated and put in the ground before a cement pad is poured... it's done all the time.

I recently saw some framing being demo'ed that was done on top of a sunken concrete floor with concrete stem walls (it was used as a stage). Unknown to anyone, there was evidence that the framing had been standing in up to 6" of water at some point. Not cool.

 

IMO, ductwork isn't really needed. It's such a small area and there will be a 6' x 8' opening into the main living space. Plus there is already a supply register right smack in front of the opening. He said I need to get a licensed contractor to do a heat load calculation for the new (50 sq ft) space. Really? I may have to upgrade my heat pump and air handler because of a 50 sq ft mudroom? Give me a break.

 

The reason I suggested this method is because the mudroom floor will be about 8" above the garage slab in order to meet up with the dining room. I figured a continuous slab could be poured from garage through mudroom then joists on top of the mudroom slab. Sounds like this is not a good idea.

So it looks like my options are either a concrete slab level with the dining room floor (no joists) perhaps with a buried duct (probably not necessary) or a crawlspace with access door, foundation vent, and vapor barrier?

 

Didn't mean it was a bad idea. If doing it that way works with the level of garage (you would need to have room for a step and landing) and level of living room, plus gets your ductwork out there, it may be a good solution.

But it may be redundant if you can pour the pad at the level of the living room floor.

As mentioned by someone earlier, a wood floor can feel warmer.

 

Insulation underneath the concrete? How is this done?

 

Oh okay. So would doing joists on top of a concrete slab be against code? Builder seems to think so. Or maybe it's having a continuous slab from garage through to the mudroom that is against code. He isn't very forthcoming. It's yes or no with him and no supporting explanation. Very frustrating.

 

Thick sheets of foam are laid on the backfill prior to pouring the floor.

There is no "code" against framing on a slab. Framing on a slab would require treated plates or a sill sealer since SPF should not directly contact the concrete.

 

Okay. So my best guess is his issue is with having a continuous slab from garage to mudroom. Although there would still be the required step-up into the living space (mudroom). I wish he would make it clear what the issue is.

 

So is a radon pump/fan/vent needed in a ventilated crawlspace? Ventilated meaning foundation vent(s) to the exterior?

 

Has there been a radon test done? Are there radon issues with the rest of your house or neighbors?
Not all houses have radon and if radon isn't collecting in the crawlspace there is no need to remove it.

 

I did a radon test a couple years ago and it came back negative. Think I may have done it twice. Immediate neighbor has a vent.

If I go the slab route (which I like the best), insulating between the gravel base and slab will keep the floor warm above? It's not too big of a deal because it's a mudroom...basically a hallway connecting the garage and dining room. In other words no one is going to be spending any time in there anyway.

 

Insulating the slab will help but a concrete floor without in floor heating or forced air vents near the floor may not be as warm as the rest of the house. IMO concrete is fine for a mud room.

 

Much of what you are asking is a matter for LOCAL codes. Unless a respondent lived in your community it is quite possible the code for them would be different than the code for you. That is why you hire an HONEST builder and architect, because they should KNOW the codes that are applicable to YOUR situation.

Adding HVAC ducts/vents to a crawl space is ONLY done when the crawl is sealed off from the exterior. If the crawl space is vented to the great outdoors then HVAC is NOT added to the crawlspace.

The necessity of radon mitigation systems is a matter of local code AND the actual presence of radon. Even if previous radon testing has been negative IF your local code calls for radon mitigation then it will be necessary.

To prevent heavier-than-air garage fumes from entering the mud room it is preferable to have the mudroom floor elevated from the garage floor. Local code where I am requires an 18 inch difference in height.

For that small an area I would certainly consider electric heat over extending the central forced air system. This could be radiant floor, baseboards or radiant ceiling. I would likely go with the ceiling if it were mine.

 

Thanks for all the feedback. I'm going to go with a slab. What about his comment about needing to have a licensed contractor do a heat load for a less than 50 sq ft area, basically a triangular shaped hallway with 6' wide by 7' tall opening to a conditoned space?

 

Again, it would be a matter of local code that would require the calculation. You could call the local building inspection office and ask. It might be the contractor has a buddy in the HVAC business that needs to make a payment on his boat or something.

 

Seems ridiculous. If you dont want it done, tell him you will assume the risk of passing on the calculation. Units are usually sized to factor in a margin of error and/or extra capacity for heat loss.

 

What exactly is the "risk"? Failing inspection?

 

If your unit is already undersized, it will not be able to heat and cool the added space adequately.

 

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Right, I'm fine with that risk. It will be okay.

My concern is passing inspection. Will the inspector ask to see the results from a manual J calculation? Apparently 29 states including Virginia require one be done for new construction.

Guess I should move this to the HVAC forum since that is where it technically should be.

 

As Furd said, these are questions you need answered locally. Call your local city inspector and ask your questions... just tell them up front what you are dealing with and that you want to make sure your contractor isn't trying to make you pay for things you don't need.

There are no requirements around here that REQUIRE that on an addition.

 

Here is the list. Nebraska is on the list, so if you're certain it isn't required, then it's probably safe to say Virginia isn't either. I'll check with my local inspector as recommended.

Alabama
California
Connecticut
Delaware
Florida
Georgia
Idaho
Illinois
Indiana
Iowa
Kentucky
Maryland
Massachusetts
Michigan
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
Oregon
Pennsylvania
Rhode Island
Vermont
Virginia
Washington
Washington DC

https://homeenergypartners.com/2012/...ed-state-code/

 

The key words there are "new residential construction." That applies to building a new house, not putting on a small addition. If you were putting on a large addition, common sense would dictate that someone run the numbers again to see if an additional or larger unit is needed.

 

I completely agree with you.

 

I just got off the phone with the county building inspection office and my builder was wrong about everything

My county does not require radon mitigation and hasn't for years, the mudroom slab CAN be on the same level as the garage slab (the code was changed several years ago since they now require the garage to slope away from the home), and no Manual J calculation is required for additions.

So, I'm going to have one continuous slab poured from garage to mudroom and build up the mudroom to the dining room floor level with 2x8 joists so I can insulate with an R-19 and run my single supply duct. Warm floor and no awkward crawlspace!