At Home In The Woods

[Obed]

We had several conversations with the framer and truss designer about the subflooring for the attic/upstairs. The house is a story and a half. However, we have no intentions of finishing the upstairs. We don't need the space nor do we really want to have to clean and maintain it. If we ever decided to sell the house we would most likely finish the upstairs to increase the resale value.

Thus, we really didn't want subflooring in the upstairs/attic. The attic floor trusses are 18" high, 19.2" O.C. We intend to use blown insulation above the main floor ceiling. Doing so will give us better insulation coverage than batting. We also would like easy access to the truss area below the attic and above the main floor ceiling for ease of running future wiring, etc. I'd rather not have to punch holes in the main floor ceiling to later add a light, ceiling fan, surround-sound speaker, etc.

On the other hand, the framer really wanted subflooring up there to make it easy for him to install the stick-built roof. The truss designer was encouring us to put 3/4" Advantech subflooring upstairs to stabilize the attic floor trusses. Note: The truss designer works for the building supply company and I'm sure also wants to sell us the subflooring.

We ended up buying cheap 7/16" OSB to use as attic subflooring. Each sheet will be screwed to the trusses with a screw in 4 corners and with one screw per truss down the middle for structural support. We will need to temporarilly remove some of the subflooring sheets when we blow insulation in the floor trusses and for running main floor ceiling wiring. The OSB subflooring will not be glued to the trusses. The cost of the 3/4" Advantech that the truss designer wanted to sell us would have been over $1200. The cost for the OSB was $400.

If we ever decided to finish the upstairs, we would add another 7/16" layer of OSB subflooring on top of the existing OSB. Keep in mind that we would only finish the upstairs in order to sell the house.

 

[radioman]

Sounds like a game plan for the what if in the future with thinner osb. The only thing I would be concerned with is how far they screw in the screws. if they countersink too far it due to being soft, its gonna be a bear find them and out, but then its too late to think about that.

 

[mikefromnh]

You will be glad to have a floor for storage. And it will save a lot of time framing the roof.

Make sure they use good quality screws such as 'Deck-mate' or other good brand name. Commodity (the kind you get out of hardware store bins) dry wall and deck screws will snap/strip easily.

 

[gpflepsen]

Whoa... I suggest strongly to put down 3/4" OSB or tongue and groove plywood. You want a stable surface that can take a load without flexing. Imagine carrying 100 lbs and stepping midspan at the edge of the thinner 7/16" OSB. I bet some audible cracking would be heard. Put down one layer of subfloor and be done would be my preference. I would definitely put something down to stabilize the trusses. The drywall ceiling will thank you for that alone.

Why are you insulating the floor, sound management? I would think the attic would be the place for thermal insulation. In the future if you want access to the truss area below the upper floor for insulating or fixture installation, you can always remove the screws and lift the subfloor from the area needing the access.

 

[nhkabotab7800]

i agree that you would be better off using something thicker than 7/16" osb 5/8" even would be better. perhaps 3/4" osb but not Advantec i understand your desire to save money and that you will not really be on the second level, but 1/2" osb is just too thin to span 2 foot on center trusses.

 

[Duffster]

i agree that you would be better off using something thicker than 7/16" osb 5/8" even would be better. perhaps 3/4" osb but not Advantec i understand your desire to save money and that you will not really be on the second level, but 1/2" osb is just too thin to span 2 foot on center trusses.

The floor trusses are 19.2 oc.

7/16 will work, you got to remember that with the floor trusses on that spacing there is only 15.7" between the trusses.

 

[FallbrookFarmer]

I think that you are going to have some bounce in the floor with 7/16 OSB, but if you ARE going to go with it, I would suggest making some sort of marks as to where you are screwing it down to the OSB. That way, if you decide to add another layer, you will be able to hit the trusses, when you screw/nail down the next layer.

 

[2manyrocks]

For what it might cost in the future to add another layer of OSB, I would go ahead and sheet the attic floor properly now and be done with it. Think about having to haul in 4x8 sheets of material into your attic space after your house is finished.

 

[gpflepsen]

For what it might cost in the future to add another layer of OSB, I would go ahead and sheet the attic floor properly now and be done with it. Think about having to haul in 4x8 sheets of material into your attic space after your house is finished.

What's the old saying... "penny wise, pound foolish".

 

[sld]

For what it might cost in the future to add another layer of OSB, I would go ahead and sheet the attic floor properly now and be done with it. Think about having to haul in 4x8 sheets of material into your attic space after your house is finished.

That is a very good point! Spend a few hundred to do it right.

Easy for me to say.