Messages and Online Forum Q&A
Re: floor that sags
There is simply no excuse for having a "bouncy" floor in a new home. Unfortunately, while the building code specifies minimum standards for safety, they don't specify what constitutes acceptable "bounce" from a quality-feel standpoint. Generally, the rule of thumb is that a floor should not sag more than 1/360-1/480 of its span under live load conditions (1/240 of span under full live+dead load). So, for example, if the joists are 16 feet long (unsupported by intermediate girders), then the floor should move no more than about 0.3 - 0.5" in the center. However, for some people, this may not feel stiff enough.
It is possible to fix this by adding an additional floor joist along side each existing joist. This may be difficult given plumbing or insulation which may be in the way. It may also be possible to provide an intermediate support in the center along with a steel stiffener.
We recommend that you contact the original builder (since it's a new home) and officially register your complaint and ask for a remedy. Be cordial bit firm. Say something like, "We just spend $X on our new home, which we love,...except that the floor is exceptionally bouncy in a particular area and you are requesting that remedial action be taken to stiffen it."
Give a deadline for a response. In the meantime, please reply with the following information if possible:
1) What is the height of the crawlspace from the bottom of the joists to the top of the soil or rat proofing?
2) What is the size of the joists?
3) What is the unsupported span length?
4) Are there any intermediate girders supporting the floor joists? Or do they just span an entire segment of the foundation?
5) What is the spacing of the floor joists? 12, 16 or 24" on center?
6) Are they "I" joists or traditional 2x material?
7) Can you tell what kind of wood it is? Are there any markings showing whether it is Hem Fir, Douglas Fir, or other type of wood?
8) Do you know how thick the plywood is on top of the joists? Can you see any markings on the plywood? (Insulation may make this impossible to see).
9) Do you see any signs to glue being used to secure the plywood to the joists? You might see some construction adhesive dripped down the sides of the joists.
All of these factors influence the strength of the floor. At least we can help determine if your structure meets minimum building codes. Then we'll go from there.