Crawspace vs Basement

[Rover]

I searched the forum and I didn't find this subject.  Sorry if I missed it.
I've been thinking about cottage design and unsure about having a basement.  Originally, I was going to have a basement with mudroom, storage & 2 bedrooms.  I'll be building in an area that has 4' of frost, so the foundations do have to go that deep.
Here are the plus-es and minus-es of having a crawlspace instead of a basement.  Am I missing anything?
+ building sits lower to ground so less exterior steps required
+ no musty rooms in a basement and no leaking basement
+ no interior stairs for when I'm older
+ better views from rooms relocated from basement
+ no need to constantly heat basement to prevent cold from getting into basement and frost getting under footings
+ less costs re less excavation, shallow foundations, no slab on grade, no granulars, no stairs
- more cost re subfloor, floor joists, roof trusses, roofing, exterior sheathing, siding
- no excess storage space although could build garage at some point if needed
- access to plumbing is a little difficult

[Billy Bob]

Hi, Rover.
It's a good idea to do these thought experiments so you are not trying to build and design at the same go.

I'm not sure about some of your concerns, basement vs. crawl space.  A crawl space really IS a basement, just not a full depth one.

There is no reason for a house on a crawl space to "sit lower to the ground" as an inherent quality. The finished height is a consideration of final grade,  the need to keep your home away from wood devouring bugs and fungi, and maybe a little aesthetics.  Or enormous rocks too big for Glenn's Bobcat. [smiley=wink.gif]

A crawl space can get plenty musty if not properly ventilated.... you just don't go in it so often to notice.  Crawl spaces can also certainly leak and accumulate water if not built/treated to local conditions.

A basement should not be heated with the idea of keeping frost from the footings;  that is just such a horrible thought, environmentally.  The reason for the footings going below the frost line is to take care of any such problems. If the local code says four feet, then the average frost is really unlikely to go deeper than about 24".  I have never seen a house where the basement was deliberately heated except for comfort when it was being used for occupied space. Foundations can be protected by insulation, as described in a couple of threads here.  Not a bad idea in any event, IMO.

A crawl space should  be somewhat less expensive than a full basement, but again there may be confusion on terminology.  "Slab on grade" usually refers to a third kind of foundation where the basement slab is poured right on ground (grade) level, and often serves as the subfloor.  Little or no excavation is done, and it is most often used in less cold areas. What I think you refer to is a finished concrete floor in the basement, which is nice but optional.  So far I have lived in or owned six different houses here in New England that had unfinished dirt or gravel floors in the otherwise "full" basements.  By the same token I have been in a number of crawl spaces that had finished slab floors.  Most of the dirt floor versions had, and needed, sump pumps.

Same point about subfloor and framing costs, etc.  There is no big difference from the mudsill up whether you use a crawl space or full basement.  There would be differences vs. the above mentioned "slab on grade", or a post and pier type foundation, in the flooring design and cost, but everything else should be close to the same.( Well, plumbing can be a PITA on slab construction)

For my money, if you have to go down four feet anyway,  the additional cost would not be that much to go a full basement.  I would put together estimates both ways.

Have fun, and good luck.

[PEG688]

Rover a crawl space is just a short foundation. If you are comparing Slab On Grade , no joist no floor sheathing to a crawl space you'll need to reconsider the options / materials used.

 
 Back east , well 25 years ago most houses got full basements , becauce the footing needed to be 4' deep like yours . So it was cost effective to dig out the remaining dirt to get a full basement .

Plus to a full basement IMO would be :but not limited to the following :

1.  Extra room.  

2.  Equip. room , furn. , water softener, well pressure tank, elec. C/B pnl, etc

3. Garage if sloped lot .

4. Lawn equip storage .

 A crawlspace is a short foundation , we use those here in the PNW mostly . sloped lots sometimes end up with full foundation / basements but generally a crawler will do.

 Slab on grade is cement poured well,  on grade , plumbing pipes need to be installed first , in the right spot   You'd be surprised how often they get put in the wrong spot   And also once installed  no changing where the toilet / sink and shower go without a jack hammer

 Down sides to SOG .

1. Plumbing changes hard to do.
2. Floor is hard for kids / babies even with carpet.
3. Floor is cold , unless in floor heating is used.
4. No storage / equip room it fights for floor space .

There justa few brief thoughts .

 G/L with your decision , PEG

[PEG688]

Good post Billy Bob  8-), you beat me  

[Billy Bob]

LOL, PEG and I must have posted at the same time.

PEG is the guy doing this stuff everyday, and has been doing it for awhile.....

What he says is as close to guaranteed as you're likely to find.

Thought of writing a book, dude?

[PEG688]

#1: LOL, PEG and I must have posted at the same time.

 #2:   PEG is the guy doing this stuff everyday, and has been doing it for awhile.....

 #3:     What he says is as close to guaranteed as you're likely to find.

 #4:         Thought of writing a book, dude?

 #1: With in minutes  

#2: Seems like every day Where'd the time go , 30 + years  

#3: No guarantees,  neither inplied nor stated

#4:  Who'd read it?  Title  "Thoughts of a old crummigon"  

[simplegrl]

"Thoughts of a old crummigon" - now that is something i would love to see on the new york times best seller list, i've learned never to underestimate the wisdom of old crummigons

[Amanda_931]

I do like the idea of no more than a couple of inches between the ground and the floor--and a house sited so it is extremely unlikely to flood!

That is kind of hard to do with a crawl space.  The kitchen addition on my Nashville house had floor joists only about 8 inches over ground level.  Oh, yes, by the time I actually saw them, they were deteriorating badly.  If I'd had the money, etc. I guess I would have put a slab under there.  

If you live in termite country (or country the--ground living--termites might invade in fifty or so years.) the rule seems to be no wood within a foot and a half of the ground.   The Formosan termites don't really care how high they have to go for food.

The straw bale and cob people get by with their usually very low to the ground houses by starting the walls on top of a stem wall, placed high enough not only to prevent damage from splashing rain or drifting snow but also the burst hose from the washing machine on the inside.  Insulating can be a bit of a trick, it can be done especially if you have 18" walls.

You might look up something called a rubble trench foundation.  It can be insulated below ground, has been used in Scandinavia, and in this country off and on for at least 70 years.

There are probably ways to deal with plumbing, but it will require more planning.  It will be harder to move the sink from one side of the room to the other five years later.  I've considered putting in a utility room with lift-up floor sections between the bathroom and the kitchen.  I gather waste and incoming water need to be separated.

[DemianJ]

I went through a similar thought process trying to decide between slab or basement.  It turned out that the excavation, labor, and concrete required to get proper drainage on my sloped site wasn't that far away from being the same price as a basement.  

I'd agree that if you've already got to go 4 ft down, then for what I'd guess would be less than $1-2K more (assuming you're not building on rock) you're gaining really cheap space.  Some other random thoughts:

+Temporarily cover the stairwell opening and you've got a dry and relatively secure workshop once you have the first floor floor platform framed.  Having a workshop saved a lot of setup/breakdown time.

+Basements don't have to be dank if they're designed right; based on what I've read, with proper grading, good footer drains, lots of gravel, high quality waterproofing, vapor barrier under the slab, and working gutters, you can have a bone dry basement.  Look into dimple sheeting or superior walls products.  A forum search should bring up info on both.  

+If you've got hot summers, then the basement allows you to take advantage of geothermal cooling.

+If you live in hurricane country, then it's a safe place to go as well.

+It can allow you to move into the house earlier than you might otherwise be able to.

+ (or maybe -) You'll find a use for that space and wonder how you could have done without it.

DemianJ

[Rover]

Thanks everyone,
I think I'll keep planning for the basement instead of the crawlspace.  I won't plan on any bedrooms there.  Just space for electrical panels, hot water tank, water pump, mud room, misc storage and sauna.  I'll talk to some subcontractors regarding making the basement waterproof instead of just dampproofing which sometimes looks and preforms like just black paint.  Thanks to Demain for the ideas.  The cottage will be on a crest and the soil appears to be good self draining stuff.  
If I can incorporate a walk out into the design it will make it more airy and inviting.  I'll keep the top of foundation walls maybe 2' above grade.  We don't have termites in the area (yet). This will help keep mice out.  
Regarding frost protection, I hope to have money to put rigid insulation under the basement slab. I'll also insulate the basement walls and ground floor joist spaces.  Then just minimal heat in the basement thru the winter.  If I loose electricity (heat) while its unattended, hopefully all the insulation in the walls & slab and the free draining material will save the foundation.  I can't extend the foundation much lower as suggested because of the cost of non standard and deeper formwork panels.
Re the plumbing rough-in.  I'll get that coordinated with the slab on grade, no problem.  If not, I should be fired from my day job.  
Thanks again.

[DemianJ]

You're quite welcome.

Here's a link to some info on the dimple sheeting:

[url]http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1138343295/22#22[url]

On a 20x24 basement it took two inexperienced people less than 2 hrs.  Material costs were about $300.  It's been up for about 5 months now (dried in for about 2) and kept the basement dry even before the gutters were up.

[Billy Bob]

Hi, Rover.

I just wanted to re-emphasize one thing for ya.... don't worry about "saving" your foundation from the cold or frost by heating it.  If you go standard forms depth you will be below frost line, (unless you're in Antarctica, or above the Arctic Circle [smiley=wink.gif]) and will not need to worry about heaving.( Wait a minute, I forgot about Minnesota.[smiley=shocked.gif])
 The concrete is otherwise pretty much unaffected by cold once it has set up.
Insulation is a great idea because it uses the ambient temperature of the earth to additionally protect your structure.  It also will somewhat reduce your energy requirements, as it will cut back conductive heat losses. It is also a one time cost, vs. pouring energy into a giant heat sink, i.e. the earth.  If the frost is truly deep and hard enough to endanger your foundation, then the frost protection insulation technique is more than worth it., IMO.

p.s. Another great thing about full basements: ya don't have to worry about the "slab on grade vs. plumbing " thing.  Again, "slab on grade" is a flat foundation poured right on top of the ground. That is why plumbing location is critical, because you can't move it around once poured.  In the full basement, or the crawl space for that matter, you can move pipes around pretty much to your heart's content.

[Rover]

Hi Billy Bob
Just thought I would clarify.  I'm not concerned about the effect of the cold to already cured concrete.  The only problem I'm worried about is coldness that is in an unheated basement, travels thru the basement concrete slab and under the footing freezing the ground and heaving the footing.  I've seen the damage.  I almost bought a half finshed cottage that had such damage from a careless homeowner/builder.  It was a great deal and I work with engineers & subcontractors for a living so I wasn't scared of the fix.  Someone beat me to it though.  This is a mile up the road from the land I bought; soil conditions look the same.  That is why I don't want to take the risk.

I was wondering about your comments on the slab on grade.  In Ontario, a slab on grade is just a concrete slab on ground at any elevation. Also called a floating slab because it isn't anchored to anything. In the pairie provinces they sometimes pour the slab and have the reinforcing run from foundation wall into the slab on grade.  Is that what you mean by a slab-on-grade being a flat foundation?  

I'm only asking because I'm curious.  thx

On an interesting note, on my warehouse project we will be pouring a slab for on grade 16" thick, reinforced top & bottom, to support the storage of containers weighing 80 tons (container footprint is 8' x 8').  The best part is that the client doesn't want any cracks.   urghhh  what a challenge

I worked on a project (not mine) where the 6th storey concrete slab pour froze because the tarps ripped overnight.  They had to chip it out because it never came up to strength.    Ouch  $$$$$