Home Foundations in the Mountains in Eastern Washington/NW Idaho

[Bevo 13897]

We are looking to build a home in the mountains. We are on a hill but the lot is flat so there isn't a possibility of a walkout basement. The builder recommends a crawl space. I've always been on slab or with a walkout basement. Any opinions on which is better - Small vacation home - Radiant heat, 2 -story, 2600 sq ft, 2 bedroom 2bath with loft and 2 additional half baths.

[TKthunder2 5059]

I mean your foundation normally depends on your soil composition.  If he is recommending pier and beam it’s likely because your soil will flex over the years which could cause massive foundation problems in regular slab if not maintained and inspected regularly.

I know nothing about that area but I would normally trust your engineer and do whatever they recommend.

[Onboard 2.0 9083]

Neither system is really better than the other if constructed properly.  Local geological conditions can determine which system is best utilized.

We build mostly crawlspaces here in the east, but I've designed homes with slab on grade foundations as well.  Crawlspace homes are typically warmer under your feet from my experience, easier to route HVAC, especially with multi floor homes.  Plumbing is easier to install with a bit more flexibility as construction proceeds as well, and future repairs, additions etc. are definitely easier .  Slab foundations should be a bit less expensive as you have less finish masonry exposed on your foundation (if any), less costs for stoops and steps, etc.

Point of clarification: The term pier, and beam is a bit misleading as it's not really piers, and beams, because your exterior/perimeter foundation will be a solid, continuous 4-6 course tall, 8-12" thick CMU wall on a continuous 20-24" wide  x 10-12" thick conc. footing.   We call them crawlspace foundations.  

You may have interior piers, and related conc. pier footings that support girders that support floor joist spans, but many contractors opt for continuous interior foundation walls as well instead of building multiple 12 x 12 piers, and pier footings supporting the girder spans. It's less time consuming to simply run continuous interior foundation walls, and more forgiving if you need to chase a point load down thru a building from the roof, and it doesn't land on a pier.

Edited November 7, 2020 by Onboard 2.0

[Bevo 13897]

41 minutes ago, Onboard 2.0 said:

Point of clarification: The term pier, and beam is a bit misleading as it's not really piers, and beams, because your exterior/perimeter foundation will be a solid, continuous 4-6 course tall, 8-12" thick CMU wall on a continuous 20-24" wide  x 10-12" thick conc. footing.   We call them crawlspace foundations.  

So, it is and isn't a crawlspace: The perimeter is CMU so you would have to remove cinder blocks to actually crawl under there? You both say it is easier to repair plumbing and such. I assume the plumber would have to cut a hole in the floor to reach it which is still obviously easier than dealing with a slab.

Do you have to seal the CMU to prevent moisture? Are termites an issue since you have space between the foundation and the interior of the home? Do they blow insulation in the crawlspace to keep it energy efficient? Does it raise the house higher above grade compared to a slab foundation? Are there problems with pipes breaking under the home in cold climates?

[CooterBrown 18288]

So, it is and isn't a crawlspace: The perimeter is CMU so you would have to remove cinder blocks to actually crawl under there? You both say it is easier to repair plumbing and such. I assume the plumber would have to cut a hole in the floor to reach it which is still obviously easier than dealing with a slab.
Do you have to seal the CMU to prevent moisture? Are termites an issue since you have space between the foundation and the interior of the home? Do they blow insulation in the crawlspace to keep it energy efficient? Does it raise the house higher above grade compared to a slab foundation? Are there problems with pipes breaking under the home in cold climates?

There will be an exterior access panel to access under the house.

Termites don’t generally cross masonry to get to wood. It has to be wood touching the soil for termites to be a problem. Usually it’s from tree and shrub branches touching roof lines. At least that was my understanding from when I had a termite treatment done years ago.

[Onboard 2.0 9083]

54 minutes ago, Bevo said:

So, it is and isn't a crawlspace: The perimeter is CMU so you would have to remove cinder blocks to actually crawl under there? You both say it is easier to repair plumbing and such. I assume the plumber would have to cut a hole in the floor to reach it which is still obviously easier than dealing with a slab.

Do you have to seal the CMU to prevent moisture? Are termites an issue since you have space between the foundation and the interior of the home? Do they blow insulation in the crawlspace to keep it energy efficient? Does it raise the house higher above grade compared to a slab foundation? Are there problems with pipes breaking under the home in cold climates?

Crawlspaces are constructed with a 24" or taller clearance from grade to the underside of floor joists. Your mason will provide a crawlspace access door in at least 1 if not 2 locations along the exterior foundation wall. Yes, the first floor will be 18-24" higher on a home constructed with a crawlspace.

It is 100% a crawlspace.  As you have an open space below the floor, making it completely accessible repairing or adding plumbing, HVAC, or wiring is mucho easier. Everything is exposed below the floor system.

Termite protection (soil poisoning) is probably just like a crawlspace application.  Termites aren't any more an issue than with a slab, maybe less as you have 24" or or separation of grade and any wood.

Waterproofing a crawlspace is not required unless the grade outside the crawspace is higher than the grade inside the crawlspace walls.  Typically waterproofing is only installed on basement homes, and then a perforated drain pipe, set in a gravel bed is run along the perimeter of the exterior wall to capture water as it percolates down thru the soil, and is routed to a sewer or natural outfall.

Insulation is installed in the cavities between the floor joists, unless you install a conditioned the crawlspace, then only the perimeter walls are insulated. This is how I design crawlspaces.   I would only install a conditioned crawlspace unless there was some reason you could not, and I cannot even imagine what that would be. You get how significant I think conditioned crawlspaces are right ?

Yes, in cold weather climates additional measures must be taken to protect pipes from freezing (conditioned crawlspace does that nicely). That's still an issue regardless of where the pipes are located. In cold weather climates you better install a generator with an automatic power transfer switch, especially in a second home or you'll have burst pipes if your power goes out, and temps dip into sub freezing.

 

 

 

 

Edited November 7, 2020 by Onboard 2.0

[Onboard 2.0 9083]

16 minutes ago, CooterBrown said:

There will be an exterior access panel to access under the house.

Termites don’t generally cross masonry to get to wood. It has to be wood touching the soil for termites to be a problem. Usually it’s from tree and shrub branches touching roof lines. At least that was my understanding from when I had a termite treatment done years ago.

They'll build mud tubes up from the soil on the face of the CMU on the interior of the crawlspace.  Floor joists sit atop a 2 x 8 pressure treated cont. sill running along the top of the CMU foundation wall in a crawlspace.  That is a termite blocking detail.  They used to place a termite shield on top of the CMU wall, That was a 12" wide strip of aluminum flashing that acted as a physical barrier between CMU, and lumber (allegedly).

I had a stack of lumber in our garage. As I've been emptying the house since it's sold I removed it all to a storage shed. There were termites in a 2 x 12 laying against the foundation wall, and slab connection. They'd eaten a good deal of that 2 x 12.  

Sitting on top of that 2 x 12 was a stack of Ipe (Ee-pay) decking boards. The termites did not touch that lumber. That is the best deck material out there for the price in my opinion.

[Bevo 13897]

10 minutes ago, Onboard 2.0 said:

Insulation is installed in the cavities between the floor joists, unless you install a conditioned the crawlspace, then only the perimeter walls are insulated. This is how I design crawlspaces.   I would only install a conditioned crawlspace unless there was some reason you could not, and I cannot even imagine what that would be. You get how significant I think conditioned crawlspaces are right ?

If the house is using radiant heat, is it by definition conditioned or do you still need to use forced air in the space?

[Onboard 2.0 9083]

2 minutes ago, Bevo said:

If the house is using radiant heat, is it by definition conditioned or do you still need to use forced air in the space?

No that's not considered a conditioned crawl detail.  Yes to needing conditioned air in the conditioned crawl, or you install foundation vents to allow air to move thru the space to keep moisture out of the space (then it isn't a conditioned crawl).

I don't know what radiant heat does to a floor, and conditioned crawl interface, but if you condition a crawl you shouldn't need to heat your floors (wood or carpet that is) because the floor temp will be pretty close to the air temp.  I'd still heat my master bathroom tile floor or maybe a covered porch that was a conc. slab over porous fill design.

[Incredulity 11876]

In the PNW the foundation walls will be formed and poured.  CMU foundations are pretty rare.  Everything in the crawlspace will be insulted.  There will be foundation vents that provide passive ventilation that need to be closed in the winter.

Ground moisture is a significant issue in crawlspaces in Western Wa and Or.  There is a pretty significant group of contractors that do retrofit crawlspace waterproofing. Eastern WA is much dryer so issues would be less common, but not out of question.

[Incredulity 11876]

Also the termites are much less common of an issue, carpenter ants are the most common wood destroying insects in that region.  Preventing infestation is similar, however  carpenter ants DGAF about a treated sill barrier.  They dont fuck with dry wood, but will eviserate wood that gets wet from minor leaking plumbing or roofs.

[TwiceHorn 32079]

38 minutes ago, Onboard 2.0 said:

It is 100% a crawlspace.  As you have an open space below the floor, making it completely accessible repairing or adding plumbing, HVAC, or wiring is mucho easier. Everything is exposed below the floor system.

 

As an engineer, I think this makes "pier and beam" type foundations superior to slab in almost every case.  I guess cost/benefit and appropriate soil conditions could mandate a slab, but the crawlspace aspect to me makes that type of foundation superior.

Of course, I live in North Texas, where the soil heaves like a mofo and I don't think a slab on grade is ever an appropriate foundation up here, so I'm biased.  Current home is on 18' belled piers.

But foundation failures aside, I have heard too many horror stories of what should be routine plumbing problems becoming massive issues because of cast-in pipes.

[Bevo 13897]

Switching gears a bit, it sounds like radiant heat is out and a conditioned crawl space is in. When I was looking into radiant heat one of the radiant heat manufacturers told me to contact a company called Hi-Velocity (https://www.hi-velocity.com). This was because radiant cooling has issues with humidity control and the expense usually drives people toward HVAC for their cooling needs.

Here is a short blurb: The Hi-Velocity System is an energy efficient air delivery system that can be designed to provide heating, cooling, filtration, ventilation, humidification and dehumidification. The Hi-Velocity SDHV (Small Duct High Velocity) System works on the principle of pressure rather than air velocity. It is quite different than a conventional furnace, the main difference being that the supply duct work is all "small diameter" or "mini duct".

Are any of you familiar with such systems? Do they make any sense? The reason I bring it up is because they push drier air than a conventional system which may be beneficial when cooling or heating a crawl space. Plus, from what I understand, the air distributes better than traditional HVAC so you don't have air blowing on you and you don't have as much temperature variation throughout the house.

[TwiceHorn 32079]

52 minutes ago, Bevo said:

Switching gears a bit, it sounds like radiant heat is out and a conditioned crawl space is in. When I was looking into radiant heat one of the radiant heat manufacturers told me to contact a company called Hi-Velocity (https://www.hi-velocity.com). This was because radiant cooling has issues with humidity control and the expense usually drives people toward HVAC for their cooling needs.

Here is a short blurb: The Hi-Velocity System is an energy efficient air delivery system that can be designed to provide heating, cooling, filtration, ventilation, humidification and dehumidification. The Hi-Velocity SDHV (Small Duct High Velocity) System works on the principle of pressure rather than air velocity. It is quite different than a conventional furnace, the main difference being that the supply duct work is all "small diameter" or "mini duct".

Are any of you familiar with such systems? Do they make any sense? The reason I bring it up is because they push drier air than a conventional system which may be beneficial when cooling or heating a crawl space. Plus, from what I understand, the air distributes better than traditional HVAC so you don't have air blowing on you and you don't have as much temperature variation throughout the house.

Interdasting.

Yeah, radiant is going to have a problem with humidity control because the heat exchange occurs right there in your room.  It cant possibly happen fast enough to condense moisture out of the air.

https://www.airquipheating.com/article.cfm?ArticleNumber=69

The main advantage of the high velocity systems seems to be avoiding the need for big ducting, so they're ideal for retrofits.  Small tubing/ducts, small vents.  

Instead of heating/cooling a relatively large volume of air moving relatively slowly, it deals with a small volume of air moving quickly.  So the cold or hot air comes into the room in a hurry, but has to diffuse into the room to effectuate temperature change.  I'm no longer capable of running those kind of numbers, but I am skeptical that that diffusion occurs faster than with a higher volume of air.  Diffusion occurs either way, but conventional hvac replaces the volume of air in the room fairly quickly so is less reliant on the cold or hot air diffusing through the room.

I also might venture that the blowers required to push that small volume of air through those small-diameter tubes at high pressure are more susceptible to failure than lower speed blower fans.  And I am virtually certain that the motors will require more power.  Where the break-even on that is, is anyone's guess.

I'd talk to someone who has one before doing that.

Of course, it would seem that you could survive in your area without AC entirely.  The interest in cooling rate and dehumidification is a southern/Texas thing.  You probably really only need to concern yourself with heating.

Edited November 7, 2020 by TwiceHorn

[Onboard 2.0 9083]

4 hours ago, TwiceHorn said:

As an engineer, I think this makes "pier and beam" type foundations superior to slab in almost every case.  I guess cost/benefit and appropriate soil conditions could mandate a slab, but the crawlspace aspect to me makes that type of foundation superior.

Of course, I live in North Texas, where the soil heaves like a mofo and I don't think a slab on grade is ever an appropriate foundation up here, so I'm biased.  Current home is on 18' belled piers.

But foundation failures aside, I have heard too many horror stories of what should be routine plumbing problems becoming massive issues because of cast-in pipes.

Yes the accessibility is a huge benefit.  I do like the look of a home that sits right  down on grade though 

[Bevo 13897]

4 minutes ago, Onboard 2.0 said:

Yes the accessibility is a huge benefit.  I do like the look of a home that sits right  down on grade though 

Maybe. I don't know if a foot or so helps, but the higher we sit on the hill, the better the views.

The last question I have on the build for now is with regard to SIPS. I haven't pushed the issue, but it seems like my builder prefers stick framing to SIPS. He pretty much dismisses things out of the standard like SIPS and MgO (verses drywall). The R value of SIPS is much greater and the cost doesn't seem to be significantly higher. I can see the downside to MgO - his drywall guys and painters are probably unfamiliar with it and it is more expensive. I'm having a hard time seeing the downside of SIPS at least on exterior walls and roof panels.

[Onboard 2.0 9083]

Can't speak to SIPS panels with a lot of authority.  I've never designed a home with anything other than SIPS for the roof.

 

but yeah if they're unfamiliar with them they'll fight you .

 

[XYZ 2154]

On 11/6/2020 at 11:19 AM, Bevo said:

We are looking to build a home in the mountains. We are on a hill but the lot is flat so there isn't a possibility of a walkout basement. The builder recommends a crawl space. I've always been on slab or with a walkout basement. Any opinions on which is better - Small vacation home - Radiant heat, 2 -story, 2600 sq ft, 2 bedroom 2bath with loft and 2 additional half baths.

You call 2600 sq.ft. small?

[Bevo 13897]

7 minutes ago, XYZ said:

You call 2600 sq.ft. small?

I tell you I gotta plead ignorance on this thing.

 

Edited November 7, 2020 by Bevo

[Onboard 2.0 9083]

57 minutes ago, XYZ said:

You call 2600 sq.ft. small?

It's smallish.