I put down a very thick plywood floor and use the attic for storage. I wanted to put self standing shelves up in the attic but a few people have asked me if this will add too much weight up there by allowing more storage space plus the weight of the shelving units. The floor is quite strong and I am not hanging anything from the roof beams. The house was built in 1994. Thank you for your help.
Thank you for your question and welcome to the community.
Linda in order to be able to give you a real and sensible answer I would need to know a little bit more about the attic you are using for the storage.
What is the size of the beams (joists) that are supporting the attic floor?
What is the span of the joists, from wall to wall?
What is the spacing in between each beam (joist) that is supporting the floor?
Is there a beam under the floor joists that is running in opposite direction and supporting the floor?
What type of plywood did you put down?
And finally how heavy are those shelves?
I will try to answer your questions to the best of my ability. I am obviously not a builder.
1. Size of the beams supporting attic floor: 2"-7"
2. Length of the beams: Hard to measure since I already have a lot of stuff in the attic, but I think that they are about 24 ft long.
3. Spacing between each beam is 14"
4. I put the floor in about twelve years ago and can't remember. I tried to look along the wall and did not see a beam running in the opposite direction.
5. I put down 1" thick tongue and groove particle board.
6. Each shelving unit has a net weight of 103 lbs. I do have the option of creating two separate shelves out of each unit. I wanted two put two of these 103 lbs units in the attic.
Thank you for your advice.
While I am not a structural engineer by any means, I would suggest using 3/4" plywood decking. I would also use deck screws to secure them to the joists, as this will keep movement to a minimum. Don't use particle board, because they aren't as strong.
As to beams, any walls running perpendicular to the floor joists in the living space below the attic will increase the strength greatly, as long as it is tied in properly.
If possible, take pictures, diagram what you can including measurements, and consult a structural engineer. While the majority of the work can be simple and you can do it yourself, this is one area you really want an expert opinion on.
Just my $.02 opinion.
I want to add that below the attic is two rooms which are divided perpendicular to the beams in the attic. The attic covers only 1/2 of my house.
Thank you for the additional info.
Can you use this space for the storage really depends on the wall that is running perpendicularly to the ceiling joists.
In other words if this wall is load bearing and it is cutting a span of the ceiling joist in half (12') you are fine to use this space as a storage.
If this is a free span and there is no mid span bearing wall i would not recommend using this space for any kind of storage.
Now let's go back to the info you have provided so I can explain in detail.
First I’m going to convert your info so you can use it yourself with the maximum span calculator I have provided a link for at the end of this post.
You said that your beam size is 2"x7”, unless this is a rough sawn custom cut lumber your actual size of the beam should be 1-1/2"x7-1/4" or nominal 2x8".
There should be a grading stamp on the side of the board that will look like this:
Most grade stamps, except those for rough lumber or heavy timbers, contain 5 basic elements:
WWPA certification mark certifies Association Quality standards and is a registered trademark.
Mill identification Firm name, brand, or assigned mill number.
Grade designation Grade name, number or abbreviation.
Species identification Indicates species by individual species or species combination.
Condition of seasoning Indicates condition of seasoning at time of surfacing:
15% maximum moisture content
19% maximum moisture content
over 19% moisture content (unseasoned)
Usually for the ceiling joist #2BTR grade its used so let’s say that you have a 2x8 #2BTR grade.
Next is the spacing that you said is 14" from joist to joist and that translates to +-16"O.C on center.
There is no tongue and groove particle board ,there is something called oriented strand board or OSB and that is most likely what you have down, as long it has a APA stamp or American plywood association approved it is fine to be used for a subfloor sheathing.
This is the link for a maximum span calculator from AWC or American wood council.
Do not use screws on T&G plywood; screws are not by code in most states because they do not allow for expansion and contraction of the subfloor.
Approved fasteners for subfloor are nails 2-1/2 8D ring shank nails in combination with subfloor adhesive.
Your allowed weight and span for a 2"x8"x12'#2BTR HEM-FIR based on the info you have provided is 20 PSF of dead load and 30 PSF of live load with minimum bearing length of 0.68".
To simplify you can place 20 pounds of dead load per square foot on your subfloor as long it’s supported mid span.
Calculate the total square footage of your shelves and divide by the weight and you will get the amount of dead load that they have per square foot.
Hope this answers your question and again welcome to the community.
Thank you for all your info and help George.