Removing exterior wall for addition
Hello,
Bottom line: I am seeking advice on how best to carry the load of my second floor with an LVL beam when I remove a 27′ exterior wall to create space for an addition.
The house is a two story colonial. I plan to remove 27′ of the lower aft wall and carry the load with 2 LVLs, with three 2′ supporting walls at either end and in the middle. The ceiling of the one story addition will be vaulted and I plan to make the LVL flush with the existing first floor [existing] ceiling. The addition will be 16’x27′.
My three top concerns are:
1) Sheer – that is, how to ensure that I have enough support to prevent failure from sheer. Buildings here (Chesapeake, VA) are required to wiithstand 100 mph winds for design purposes. I will have the three 2′ supporting walls spanning the 27′, and another 20 feet of wall that will not be removed to aid in resisting sheer. What is the best way to get the most sheer strength out of the 2′ sections?
2) Footings – I believe I must drill into the existing footing and epoxy rebar that will extend into the new footings. For solid ground, I estimated that I would need 3 sq ft of footing for each of the three 3′ suporting walls (the ones supporting the LVL). That is based on 70# load (40 for 2nd floor and 30 for attic I believe). Is that enough?
3) Attaching second story floor joists to LVL – I plan to remove the drywall from the inside of the wall to be removed, then jack up sections of the second story enough to get joist hangars between the floor joists and top plate. I plan to fasten the joist hangars to the rim joist then bolt the rim joist to the LVL. Then, to prevent separation, I intend to strap at least every other joist to the LVL. Is this method adequate? Is it overkill?
Realize this is a lot to ask, but any advice would be greatly appreciated!
Regards,
Bill
Replies
Sheer - as I understand what you're doing, the three 2' sections need to provide all the sheer resistance on that wall. Your building department will have very definite requirements that probably require at least epoxying large diameter all thread into the foundation walls tied to seismic anchors on each corner of the 2' sheer wall - probably at least a doubled stud on each side and well nailed ply/osb on one or both sides. If that won't cut it, there are premade sheer walls for situations like yours - all with varying ratings based on your need. Every part of short sheer walls have to meet the required detailed specs to pass inspection.
Hangers - If you use long hanger nails that will help to firmly connect the lvl to the rim your hangers are going into. Rather than trying to jack the second story up to get your hangers in I normally put 4 new 16d nails in the end of the joists through the rim just to hold it temperarily, cut out the top plate and add your hanger. There really isn't as much pressure on the floor joists as you'd think and not having a plate for support isn't a big deal - if a joist does droop a tiny amount it's easy to wedge it back up, but I'll bet most don't move at all.
With long sections of wall being taken out with finished 2nd story space above, it's important to keep the 2nd story rim joists (and everything else up there!) in alignment - after the sheetrock is cut back to access the ends of the joists I'll run a tight string line of 100 to 200 lb spider wire fishing line (very small diameter, very strong, no stretch, no sag) spaced 1/4" off the framing with a few 1/4" drive screwdriver bits between the line and bottom of the framing - rather than try to tie it off with a knot - hang a weight off one end of the string - a 5 lb (hammer, drill, rock, or board) would be about right for your situation. At each stage you can see how level everything is - often you'll want to adjust things slightly up with a stud wedged in here or there - this method allows an easy way to judge the slightest movement across the entire distance. In a case like yours I think of it as a requirement - otherwise there is no way to easily tell if the entire wall has settled.
I don't understand the foundation description so can't comment.
sheer etc
Thanks Don. That's a huge help!
As far as the footings are concerned, I am really just interested in calculating the appropriate size that is required to distrubute the weight of the whole 2nd floor., attic, and roof through just the 2' wall sections.
Thanks again.
Oh I get what you're saying now about the footings! How tall are the stem walls directly above your current footings? In many cold areas our footers are pretty deep and the tall stem walls distribute weight over a large area so we normally don't have to modify a footing in your situation. From a point load if's often allowed to consider the load will spread at a 45 degree angle down through the stem wall and footer - so if you're 5' from the top of foundation to bottom of footer you can count 5' of footer in both directions.
In situations where that comes up short any footer "wings" attached to the side of the existing footer need to have an engineer's design and stamp ($500).....you may choose a low tech way to widen your existing footers buy digging out a section under the footer - say 3' x the width you need x 1' deep - and pour concrete under the existing footer. Then dig out another section and repeat under the areas you need the additional support. Again, think of the load being distributed in a 45 degree angle so the depth of the new footer will depend on what's above it and how wide you're going. You're normally allowed to consider the load spreading ability of the existing footer so if it's 16" wide and 8" deep and your going a foot wider on each side then the new concrete needs to be as deep as it is wide and you'd pour it a foot deep. If you only need to go 6" wider on each side, then it only needs to be 6" deep - although it's difficult to dig out and repour something that thin so I would just make it a foot anyway.
If the new footer sections have enough extra concrete to somewhat wrap around the existing footers a few inches many building plan reviewers wouldn't require additional pinning of the old and new with rebar - not that it's going anywhere anyway.
If you dig out a section and the existing footer is cracked up enough to want to pull away from the stem wall you need to jack it back up so it's solidly against the bottom of the stem wall. I use the 1' square concrete post pier bases sold with a hole in the top for an adjustable post base - the ears of the post base are bent flat and it's all put under the footing and pressure is applied - then it's simply left in the hole and covered with concrete. You could also use an automotive jack on top of a concrete block, or a cut down lally column if you have an extra one you need to get rid of. You get the idea.
I knew one engineer that wrote the specifications for adding "wings" to an existing footer that needed a 3' square footing - it involved all kinds of epoxied in rebar, not just in the footer but also in the stem wall and forms that were a pain in the butt - the pour was a square cube of concrete wrapped around a section of existing foundating 3' deep, 3' tall, 3' wide - more work than digging under the area I thought, and a lot more concrete.
edit: a building plan reviewer won't require an engineer's stamp on a footing underpour, so you save the $500 engineering fee.
Footings and LVL
Don,
Your a regular fountain of knowledge. Thank you!! I think I can make do w/ the 45 degree rule of thumb. My knee wall is about 3 feet, but w/ a 2' wide wall and a 3 sq ft footer requirement, I should be fine.
Your previous response concerning the spider wire and fastening the joists to the rim joists before hanging them w/ hangars - after "hanging" them, would I have a problem gluing and bolting the rim joist to the LVL? Or, would I need to catch/strap it somehow underneath?
Thanks again!!