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Is this design plausible/do-able?

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May 18, 2014, 09:39 AM
Colt Hero
Is this design plausible/do-able?
Southeast: Raised slab (4 CMU tall), drainpipes directly out exterior walls and connected together *outside* footprint perimeter (all baths on exterior walls), 2nd floor flooring would be trussed with (split) HVAC running through trusses possibly blowing both ways (up and down). Would like to stick build the roof since there is living space on 1/2 floor above. House is 1 1/2 story ranch comprised of two boxes: Main box is 32' across front by 32' deep. This is Family Room in front and Kitchen/Dining area in back. To the left is a rectangle of bedrooms and baths (on exterior walls) which is 28' across the front by 46' deep. Roof is Saltbox over Main box with 2nd Family Room under roof, and standard gabled roof over bedroom rectangle. There is also a breezeway coming off the main box at the kitchen going to a 2-car garage.

Want to minimize piping buried under raised slab, hence baths (and all water) on exterior walls.

Want to put HVAC ductwork into flooring/trusses as opposed to running overhead in attic (to maximize usable space on 2nd floor).

Want to stick build roof to maximize space on 2nd floor, but can this be done on top of trussed floor?
May 18, 2014, 11:26 AM
Jaybee
Everything you want to do is fairly basic and can be done, but like all things there can be good and bad:

1. Plumbing on the exterior walls invites all sorts of problems. The obvious freezing issues can be countered by making thicker walls (2x6 vs 2x4). This along with proper instillation of the plumbing will give enough insulation on the outside of the plumbing to avoid most freezing issues - especially in the Southeast. However even with that be aware that the chances of having a plumbing issue with your plumbing run in the exterior walls is much greater than having a problem with plumbing buried in the slab.

Another downside will be cost. Running all plumbing to the outside walls will be more expensive to install, both in materials and labor.

Have you considered building a crawl-space rather than on a slab?

2. Running ductwork within floor trusses makes perfect sense and is done all the time.

3. Stick building the attic / upper floors is usually the only way to get that 1-1/2 story living space. It's going to cost more to build compared to roof trusses. The best compromise will be to use engineered trusses in all areas that you can and stick build the rest.

Only other thought is just one on design - an open breezeway is not as nice to use nor as secure as a closed passage to the garage.


Jaybee
May 18, 2014, 01:39 PM
Colt Hero
Jaybee,

Thanks for your response. I was trying to keep my post as concise as I could, and I guess there were some loopholes:

I am planning on 2x6 exterior walls. Possibly even some 2x6 interior walls where I'd like to run bath sink drains toward exterior wall before connecting to toilet main line. Idea is to minimize PVC piping below floor in case of plumbing problems down the road. Will also be adding extra vertical cleanouts on the exterior for maintenance purposes. I realize the cost will be greater bringing piping from both ends of the house and "Y"-ing together before going to street, but that's the only way to minimize burying the piping below the slab with the "Y".

I *have* considered a crawl space. In fact, I've gone back and forth 100 times on this in my mind with all the pros and cons. It's always been crawlspace for this house - until they recently changed the rules to require "engineering" (which adds at least $2000). Not a deal breaker, but then when you add this to the drawbacks of the crawlspace: no useful space in this 3' height, mold growth, bugs, etc. versus the advantages: better PVC access, softer floor, the raised slab looks better and better (as long as you minimize the buried piping). Plus, I find that in the Southeast, the wood subfloors don't really hold up over time. Subflooring starts to warp in the bays with the joists forming peaks over time. Then you've got all the squeaking (unless screws are used), rotting around bathtubs, etc. I've finally concluded that if you're not getting a basement, and your crawlspace is going to be a dirt floor, might as well pour the RAISED slab - but with localized and minimized PVC running through it. Then, put in plenty of wiring in your walls. Also, HVAC in crawlspace is dirty - that's another negative.

As far as trusses, I really don't like them, but with the slab, I feel I need an efficient way to run the HVAC duct work and the floor truss does that. For the roof, I dislike trusses even more because they just waste so much space (although they probably give the stronger roof). Stick-building a roof on top of trusses can give truss manufacturers pause, however. Not sure if it's really a structural issue they have (because they don't know how the loads from a stick-built roof will affect the floor trusses), or if they're just telling a story to sell the roof trusses along with the floor trusses.

The breezeway *will be* enclosed to the garage. I guess I worded that vaguely? It's a one-story breezeway. Wanted a 2-story so you could walk from 2nd story of main house across to garage, but Saltbox on main house doesn't seem to want to cooperate. As it is, I might have to lower that 2nd floor back wall to 7' just to ensure at least a 5/12 pitch on the short Saltbox roof section in the back. Want at least an 8/12 on the front (with 3 dormers poking through).
May 18, 2014, 02:37 PM
Jaybee
quote:
Originally posted by Colt Hero:
Jaybee,

Thanks for your response. I was trying to keep my post as concise as I could, and I guess there were some loopholes:

I am commenting based on being a GC in the Southeast. A lot of what you want to do and the choices you describe come down to "this way will work and so will that one". Neither is wrong and as you already know, each has some advantages and disadvantages.

I am planning on 2x6 exterior walls. Possibly even some 2x6 interior walls where I'd like to run bath sink drains toward exterior wall before connecting to toilet main line. Idea is to minimize PVC piping below floor in case of plumbing problems down the road. Will also be adding extra vertical cleanouts on the exterior for maintenance purposes. I realize the cost will be greater bringing piping from both ends of the house and "Y"-ing together before going to street, but that's the only way to minimize burying the piping below the slab with the "Y".

The 2x6 interior walls are a good idea. You may still get 'trapped' by doorways for the drain lines though. In my experience, the only consistent plumbing problem with a slab is deterioration of copper lines inside the concrete. I've rarely seen any PVC in slab problems other than in cases of catastrophic slab failure. So you could run your supplies entirely within the walls and run the drains down into the slab. Again - you will have more plumbing problems down the road with lines in exterior walls as compared to problems within the slab - I just can't emphasize that enough. If you have any qualms about your in-slab plumbing runs, then adding in a run of rebar on either side of the plumbing will just about insure that there will never be any settlement issues in that area that could break the pipes.

I *have* considered a crawl space. In fact, I've gone back and forth 100 times on this in my mind with all the pros and cons. It's always been crawlspace for this house - until they recently changed the rules to require "engineering" (which adds at least $2000). Not a deal breaker, but then when you add this to the drawbacks of the crawlspace: no useful space in this 3' height, mold growth, bugs, etc. versus the advantages: better PVC access, softer floor, the raised slab looks better and better (as long as you minimize the buried piping). Plus, I find that in the Southeast, the wood subfloors don't really hold up over time. Subflooring starts to warp in the bays with the joists forming peaks over time. Then you've got all the squeaking (unless screws are used), rotting around bathtubs, etc. I've finally concluded that if you're not getting a basement, and your crawlspace is going to be a dirt floor, might as well pour the RAISED slab - but with localized and minimized PVC running through it. Then, put in plenty of wiring in your walls. Also, HVAC in crawlspace is dirty - that's another negative.

The engineering requirement is new to me, other than load and span information that has been around for years. I'd be interested to know what city you are in? It could be that the engineering requirement could be easily met - or it could be that you are being treated as a homeowner and not a professional builder so they are sticking by the book. Usually, just specifying your framing size, lumber type and spacing and backing it up with span charts is enough. If you choose to use floor trusses then it is very easy - code departments recognize the engineering qualifications of the truss design company. At the worst case, a private engineer could review your plans at a cost of just a few hundred dollars.

As for subfloors in the Southeast - If there is a water issue in the crawlspace or if there is no vapor barrier in place, then the subfloor problems you list are likely. However, if the crawlspace is built and vented correctly you will not have these types of subfloor problems.


As far as trusses, I really don't like them, but with the slab, I feel I need an efficient way to run the HVAC duct work and the floor truss does that. For the roof, I dislike trusses even more because they just waste so much space (although they probably give the stronger roof). Stick-building a roof on top of trusses can give truss manufacturers pause, however. Not sure if it's really a structural issue they have (because they don't know how the loads from a stick-built roof will affect the floor trusses), or if they're just telling a story to sell the roof trusses along with the floor trusses.

As a contractor, I'd say you need to get over your truss bias! Smile Both floor and roof trusses are going to out perform stick built both for final product and in cost of installation. For the roof especially, you can save thousands on labor for the roof framing with trusses. True, you will need to stick build in areas that will also be living space - although there are trusses that can be designed for this. It's just that the truss design will be more limited than what you can stick build so it may not fit your floorplan.

There is no issue whatsoever with using some trusses (be it in floor or for roof) and doing some stick building as long as all framing meets the engineering specs.


The breezeway *will be* enclosed to the garage. I guess I worded that vaguely? It's a one-story breezeway. Wanted a 2-story so you could walk from 2nd story of main house across to garage, but Saltbox on main house doesn't seem to want to cooperate. As it is, I might have to lower that 2nd floor back wall to 7' just to ensure at least a 5/12 pitch on the short Saltbox roof section in the back. Want at least an 8/12 on the front (with 3 dormers poking through).

Sounds good. Just voicing my own personal preference about remaining indoors from the garage to the house.

You are certainly on the right track with this and have thought through a lot of the potential problems. If you are using a contractor then they can also provide you with lots of these answers and give their opinion of which method will work best in your case.



Jaybee
May 19, 2014, 12:59 PM
Colt Hero
I'm in NE SC. They change the building requirements every year here, it seems. About 5 years ago, the county tried to incorporate wind load building requirements typically seen at the beach with cables running from the footings through the external walls. Might've been some window changes and sheer wall upgrades, too. Can't remember. Builders got together and got all this stuff thrown out. But now the county is apparently on the warpath again with the need for an "engineered plan" if building a crawlspace, but not for a raised slab. I don't think anything has changed as to what you need to *do* (24" wide footings w/ double horizontal rebar, continuous block foundation all around w/ vertical rebar every 4' and filled with grout, bond beam at top with single rebar filled with grout, bolted sill plate, termite break, hurricane straps to rim joists (or in place of Hurricane Straps - I think there is a more efficient bendable metal plate that goes underneath the bolted down sill plate then is turned up and nailed to the external side of the rim joist ... but it's patented and requires royalty payments). Even with this plate, might still need *some* hurricane straps near corners, not sure.

Speaking of the crawlspace, my idea there was to build the house as if it had a basement: 3" slab on the floor, no vents in the foundation, condition the airspace just enough to avoid mold growth, then conventional wood floor system above. This way, you still have access to utilities and piping below with no buried pipes in slab or walls, and airspace between wood floor and slab below.

Would be nice if water heater could go down there, too. Is there such a thing as a horizontal water heater? Could also do "instant" hot water since lot has natural gas.
May 19, 2014, 10:01 PM
Jaybee
The 'finished' crawlspace is a great idea - only downside is the cost.

As to the water heater - We had a similar issue with a small house we were building. Crawlspace only 2-1/2' to 3' high and no room in the house for the water heater.

When we excavated for the footers, we dug out a pit to hold the water heater. Poured a concrete bottom and sides and had a drain in it. Water heater could be muscled in to the crawl sideways and then set down into the hole.


Jaybee