Hello,
I’m trying to guess what my basement/1st floor construction might look like.
My house is 36′ wide and about 76′ long. I’ll have a basement that probably won’t house much more than the mechanical and electrical rooms initially. I’m not too worried about putting in support columns as necessary – although I would like to have some 16′ x 16′ areas without columns for future rooms.
Any thought – would I need a floor truss below the first floor above the basement about 24″ in height to support l/480 at 16″ OC – can I do anything with cross support or support columns to reduce the height or improve the stiffness?
I’m not an architect or engineer and am probably at least a year away from being ready to see either – this is just a starting point.
Assume an empty basement initially and i don’t know if it matters at all but I’ve got a floorplan for the first floor.
Replies
It all depends. (where you are, is there a snow load to figure in, will you have a second floor, will the second floor have floor trusses, or will you have some of the first floor interior walls as load bearing. Will the roof be made of trusses to carry loads to the outside walls? Will you plan for attic storage, or rooftop solar or heavier roofing materials?
Trusses are great for longer spans, and also to allow you to plan for HVAC ducting and plumbing and wiring runs inside the truss openings (planning ahead is good.)
Your truss supplier can provide specific options. You can include beams to shorten spans, and support columns to hold the beams up. You can also plan a support wall to hold up the trusses mid-span (or at an offset if you like)
Some other things to think about are the location and grade of the building lot. is the soil conducive to deep basements? Is there an option to gravity drain the perimeter to daylight for a deeper basement? Would you like a slightly elevated porch and/or deck at the first floor level?
With floor trusses, stairways need to be longer. This may or may not be a concern.
If I use shorter spans - could I use a cross truss with columns to hold it up? It seems that is what some people do with dimensional lumber.
There are at least a dozen ways to do it.
https://www.mitek-us.com/wp-content/uploads/uploadedFiles/_RedesignSite/Content/documents/engineering/tech-articles/getting-started/TECH2-%20wyntk-%20Truss%20facts%20for%20eng%20and%20arc.pdf
You can use shorter span trusses (half or a third your original 36 foot span), or long ones designed for intermediate support.
The intermediate support can be another truss, or engineered lumber products, or steel beams. These additional supports can be sized to carry the whole load side to side, or for intermediate columns. (most folks use columns to reduce the size, expense, and weight of the supports. )
You can also build a wall to hold the floor trusses mid-span, and split the basement into two more or less equal parts. (the wall can have doorways as long as headers are sized for the loads above)
An important thing to understand is that all these members are designed with capacity and deflection under load as primary considerations. (along with cost, ability to ship, handle, install, and secure into the structure.
Thanks -
There will be snow in the area.
The second floor is an attic - that I'd like somewhat useable for storage although I certainly don't need much access to any area with less than 5' of ceiling clearance. Proably just a 5/8" plywood covering. The attic will use closed cell insulation on the interior.
I would imagine the attic or roof trusses would carry the weight to the outside walls.
The basement will be in area that will be conducive to deep basements. I'm sorry - not familiar with the terms but there will be a french drain around the exterior.
I would like a slightly elevated porch on the back of the first floor.
You are correct about the stairs!
Any additional info you can give would be great as I'd like to sound a little less like an idiot when I actually see an architect. While I don't expect to do his work for him, I'm the kind of guy that likes to know about HP, braking distance, turn radius, MPG etc about a car before I go shopping even though I couldn't fix an engine if my life depended on it.
I've included a guess at what I'll need in the basement. The circles are ligh bulbs, I don't have any columns yet.
The roof trusses can also be designed for intermediate supports, like an intermediate load bearing wall. (in addition to design that transfers loads at the outside walls only)
Roof trusses are a little easier because no one complains much if the roof moves a bit when you walk on it.
https://www.oregontruss.com/wp-content/uploads/2017/02/Oregon-Truss-Floor-Truss-Info.pdf
Light reading. you can google up as much more as you like.
Clear spans are great for maximum flexibility, but these solutions come with extra costs. (in money, and as you figured out, more space between floors)
Other things to think about is what kind of windows you want in the basement, and if you want to see daylight out of them, or the inside of a window well.
https://www.finehomebuilding.com/?s=floor+truss
Other good reading above.
Thanks!
I honestly don't know what the land slope will be yet. With any luck I'll have a walk out basement. I'm pretty sure no matter what I'll be required some eqress windows depending on code although I will have a basement well staircase. I haven't picked a lot yet.
The elevation of the first floor over the ground level is a consideration. basement windows are brighter if they are above ground level.
a sloped lot can be nice for having a walk-out, and for peace of mind gravity drainage, but can be a challenge for landscape maintenance.
Do the design work for your future basement plans now and build in the bearing walls initially. This will save you material cost now and headache later. If you want a bathroom down there later put in the sewer pipes now. Do the egress windows if you want a bedroom down there. If you build now with a slab and columns you are limiting your future options, most likely increasing your costs, and providing yourself no benefits that I can see.