1. In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. If the air distribution is in the attic space, then consider insulating the rafters to move the distribution into the conditioned space.
Sunroom Part 3 – Floor Trusses or How to Replace a Floor Joist
4. Apply insulation to floors above unconditioned spaces, such as vented crawl spaces and unheated garages. Also insulate (4A) any portion of the floor in a room that is cantilevered beyond the exterior wall below; (4B) slab floors built directly on the ground; (4C) as an alternative to floor insulation, foundation walls of unvented crawl spaces. (4D) Extend insulation into joist space to reduce air flows.
Years ago, while working as a carpenter, I helped stiffen a bouncy floor by nailing a new 210 to each of the 210 joists that supported the floor. It was a complex, expensive job: Working in the unfinished basement below the bouncy floor, we had to remove the plumbing and electrical lines running through the joists and then rerun the lines after the new 2x10s were in place.
As a joist bends downward, the lower edge bends slightly to one side or the other. A layer of 3/4-in. plywood firmly fastened to the undersides of joists helps prevent this side-to-side bending and stiffens the floor.
The longer the distance a joist spans without support, the more it will flex. By building a wall under joists, you divide the span. The floor above will be stiffest if you place the wall in the middle of the joists.
If your floor is sloping towards an outside wall, but your foundation has not moved, this indicates that your sill plate is damaged or compromised. The sill plate is the piece directly on top of your concrete foundation, and it has to be replaced if faulty. To replace the sill plate, jacks are installed to temporarily hold up the floor joists, until the damaged sill is removed and replaced. Costs for sill plate repairs are $100-$120 per linear foot.
When your floor drops, dips, or slopes, it often means you have sagging floor joists. Because the ends of floor joists rest on the sill plate, water damage often spreads from sill plate to floor joist.
These notches weaken the joists and cause them to crack, split, or fail. Sagging or damaged floor joists need to be sistered to be repaired. When a joist is sistered, a healthy board is run parallel and attached to the faulty one, to transfer the load. Sistering to repair floor joists costs $12-$14 per foot.
Like the sill plate, the band board is often exposed directly to the outside air. This increases the odds of it being damaged by humidity. But like the floor joists, rim joists are best repaired by sistering it.
This is because replacing a band board would require excavating around the perimeter of your house to access it. It is faster, easier, and less invasive to add a supporting piece from the inside of the joist box. (The joist box is the open space between floor joists on top of the sill plate.) Sistering a band board costs $40-50 per foot.
There are support columns set under the center beam that help to hold it steady. The distance between these columns can vary, depending on the building codes at the time your house was constructed. If the columns have cracked or broken, they will need to be replaced using adjustable steel floor jacks.
For repairs with adjustable steel jacks, please be aware that the floors will not immediately return to level. Jack adjustments are done in small increments over time; attempting to expedite this process can cause damage to your home and all the flooring. Our goal at Acculevel is to help people, and part of that is being honest and clear about expectations.
If you notice uneven floors, sagging floors, or a floor rotting from moisture damage, you may have a damaged floor joist under your feet. Joists are long beams under your floors that support the weight of your home and provide vital stability.
It will typically cost between $1,000 and $10,000 or more to repair floor joists, depending on the extent of the damage and the size of your room. Noticeable issues should be addressed so you know whether the damage needs to be repaired immediately.
Between materials and labor, structural repairs to your flooring run $40 to $60 per square foot. Joist repairs tend to run $10 to $67 per square foot, depending on the extent of the damage. You may spend more than $20,000 if all the flooring in a room needs to be replaced.
This is your top layer that usually consists of carpeting, ceramic tile, hardwood plank, vinyl, or laminate. Repair costs $130 to $2,300 to install per room or $2 to $30 per square foot, depending on the type of flooring you own. Full replacement costs $800 to $10,000 or more per room, depending on your install type.
Under your floor covering is a surface, usually of plywood, that covers your joists. Subfloor repair costs $500 to $700 per room or $2 to $10 per square foot. Full subfloor replacement costs $1,800 to $3,000 per room.
2x10 joists of softwood lumber reign as the most popular choice for floor joists due to their lower cost and their ability to be cut according to length. While 2x10s are easier to cut and manipulate than engineered floor joists, they tend to warp or bow over time due to their natural wood construction.
Jack up your floor frame from below and place a beam across the damaged joist and neighboring joists for additional support. If your sag is significant, do this slowly at about one-eighth of an inch per month.
Once the floor of your sunroom is insulated, you can turn your attention to the walls. You may not have much wall space in your sunroom, but it should all be insulated to help maintain a comfortable living temperature. Approach each section one at a time and take as much care in insulating as you did in the floor.
Dave, An uninsulated floor -- especially an uninsulated floor with radiant heat -- makes me cringe. If you can't install a continuous layer of rigid foam under the radiant PEX tubing, at least consider installing vertical rigid foam at the perimeter of the sunroom foundation. Ideally, you would dig a trench down, at least 18" or 24" deep, to install the vertical rigid foam, and would extend the foam up to the bottom course of siding. You would need horizontal Z-flashing at the seam between the top of the vertical foam and the bottom course of siding, as well as some type of durable material to protect the above-grade portion of the foundation insulation from abuse.
How deep are the joists? I was imagining that it was 8" from the dirt to the subfloor, with perhaps 2x6 joists, but now I'm thinking you have the joist depth to consider as well? With 2x10s or 2x12s and 8" under the bottom edge of the joists you're looking at about 0.7-0.8 cubic feet of volume per square foot of floor.
Taping the seams of the subfloor for any new flooring would make an excellent top side air barrier, but a sheet of housewrap would be almost as good. Preserving at least some ability for the deck & joists to dry toward the interior would be prudent (ergo no vinyl flooring or sheet polyethylene layers, no foil clad above-the-subfloor type radiant floor system such as Roth Panel, etc.) Plywood subfloor with hardwood flooring would be fine.
Dave,I don't think your plan will work. The main reason it won't work is that you can't install a layer of horizontal rigid foam above floor joists, because the floor joists will dig into the compressible foam.
I was referred to her when her tiling was about halfway done and convinced her (read: begged) her to save the remaining floors because they were not beyond repair. A week later after replacement boards were installed and the floors were refinished, she had what looked like new floors!
Hey Scott,Our Historical Society is restoring a 1870 home. The hardwood floors are nailed straight to the joists and need some repairs. One of our members says we should remove all of the flooring, put down an underlayment an then reinstall the original flooring. Do you think this is a good idea, or should we just spot repair the floor where it needs it?Thanks,Greg
Make a couple of wood stakes and put them where the corners are going to be. Use the 3,4,5 method to make sure the building is square. Once the corners are marked, figure out where the support posts should go. In this particular build, the sun room was going to have a cathedral ceiling, so one of the support beams had to be placed right at the edge of the sun room. This is because there needs to be a post going from the floor of the sun room up to the bottom of the ridge board and that needs support from underneath. Otherwise, put the row of support post one foot in from the outside edge of the structure
Prepare your support beams and place them on the support posts. In this case,the city required three ply 2 x 10's for support beams. These should be exactly the width of the exterior of the house, in this case 14 feet long. Again, make sure that the setup is square using the 3,4,5 method. The great thing about screwpiles is that they come with brackets and height adjustments. Calculate the height of the joists and flooring and adjust the height of the support beams so the flooring will end up even with the flooring of the existing house and then bolt the screwpile brackets (or sonotube brackets) to the support beams.
Frame the floor. Your city will tell you what size of lumber is required for the framing. In this case the floor joists were 2 x 10 with triple ply 2 x 10 around the outside. Bolt the ledger board (the one against the house) to the board of the existing house or through the block or basement wall if you are below the joists of the existing house. Put one bolt between each joist. Cut blocking to fit in between each joist and made rows of blocking. Attach the joists to the ledger board with joist hangers and attached the joists to the support beams with hurricane ties. Some cities only require that you nail the joists to the support beams. 2ff7e9595c
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