Shopsmith Forums

I am in the process of insulating a new 30x50x10 woodworking shop. The electrical outlets and lighting have been installed. The 2x6 stud-framed walls are finished with R-19 faced fiberglass batting and covered with OSB. I am now debating on how to do the ceiling overhead. The 2x4 roof trusses are on 4-foot centers with 2-foot on center purlins. I could line the overhead with metal sheeting for a ceiling and have blown insulation installed on top of the metal sheeting; or I could use faced fiberglass batting attached to the purlins leaving the trusses open and no ceiling per se. Would anyone care to offer opinions or ideas?

I don't know for sure but I think you are calling the roof rafters purlins.

A purline is like a girder that spans the roof rafters.

In a truss system you have ceiling joists (also called tie beams), common or roof rafters, a queen post or two, and a number to struts.

The ceiling joist or tie beam runs horizontal between the walls. Their job is to keep the walls of the structure from pushing out. The common or roof rafter run vertical on an angle from the wall plate to the peak of the roof. The queen posts are vertical studs that run between the ceiling joist and roof rafters.
And the struts run between the queen posts and the roof rafters.

Purlins usually are on top of the roof rafter to hold the roof sheathing.


That all said I think you are asking should you nail something to ceiling joist and lay insulation on top of it or insulate between the roof rafter and have an opening the whole way to the roof.

I would go for insulating the roof and letting the ceiling open you can always use overhead storage.

The only caution is. Most ceiling joists are engineered for one thing tying or holding the walls from spreading. They usually have a very low rating on actual weight sitting them.

I have seen more than one garage ceiling laying on the car after the ceiling joists broke and everything stored on them came down. In a extremely rare cases the whole roof came down in spots. NOT PRETTY. But very profitable to the contractor hired to fix it.

As I said I would go the open ceiling route and if you plan on storing much nail some 2x6-2x10 (depending on the span) beside the ceiling joist and setting on the walls.

You may have to cut some slight angle in them to get them up if you do this after the roof is on.

But you can cut the angle enough to side them back and then lift the other end and place it on the wall. You only need about 2 inches of wood on either end to be sitting on the wall.

The roof truss/joist W triangles rest on top of and are perpendicular to the east/west walls and span 30 feet without any other support underneath. The roof pitch is 4/12, therefore a 5-foot roof peak. The perlins are on top with the roof sheathing attached.

Would R-19 faced fiberglass batting be decent enough or should a higher R-value batting be considered?

If you have gable ends, I vote fer the batts since that allows summer interior ventilation(I have heard it tends to get warm in Kansas in de summer).

However the close proximity to the roofing may create a lack of ventilation there. Do you have ridge vents?

Consider adding 'perlins' on the lower edge of the truss for batt attachment?

I agree with what others have said - I would insulate the rafters and leave the space open, both for ventilation and also for potential storage. As noted, don't go crazy with storing tons of heavy things up there as you could compromise the trusses but it's always great to have extra storage. I have a couple of aluminum ladders up in that space in my shop, as well as rolls of copper tubing, stacks of tarps, a couple B&D WorkMates and other items that are bulky to store elsewhere but are nice and out of the way yet easily accessible when needed. Also. not sure what your lighting is but I was able to hang florescent fixtures up in that space so they sit flush with the truss joists, rather than having to hang down from a flat ceiling if you went that route.

I don't know.

This is a dusty wood shop, right? If you leave the rafters open, is the dust going to tend to collect up there?

I think I would prefer a "ceiling".

Hi,

If you are planning your shop to be an all season shop, meaning at least heating it then I'd for go any ceiling storage and insulate like you would a home.

Take a look here for at least a starting point.

http://www.naima.org/insulation-knowled ... alled.html

The R value has been going up over the years. Here in IL the number for the ceiling was R-30 now R-38 to R-60. Now that might be over kill for a shop but if I were building a shop right now I'd be generous with the insulation.

Also make sure you have the vapor barrier you need installed correctly. Wet insulation is not a good thing from the insulation value to mold.

Would I be correct to assume this is part of a larger building?

Ed

Don't know if this idea is too mediocre for your wants, a friend suggested to me that I just lay sheets of sheetrock on top of the 2bys and lay insulation on top of those as I work my way across the ceiling. It allows me to keep my fluorescent lights tucked between the bays and if I do decide to make a more permanent ceiling solution, I have most the material on hand.

This is neither elegant nor permanent, but allows me to semi enclose the space.

Evidently you were using the term purlins correctly and I apologize for my dissertation on roof/truss construction.

Remember a truss is engineered and constructed to hold up the roof not hold weight on the ceiling joist. 30 foot span is not going to hold much weight. As I mentioned before I have seen more than one garage ceiling laying on whatever was in the garage.

What I would do is put in a ceiling and lay insulation atop it. That would be the cheapest.

With a 30 foot span and the trusses 2 feet on center I would forgo overhead storage idea.

Ed in Tampa wrote:Evidently you were using the term purlins correctly and I apologize for my dissertation on roof/truss construction.

Remember a truss is engineered and constructed to hold up the roof not hold weight on the ceiling joist. 30 foot span is not going to hold much weight. As I mentioned before I have seen more than one garage ceiling laying on whatever was in the garage.

What I would do is put in a ceiling and lay insulation atop it. That would be the cheapest.

With a 30 foot span and the trusses 2 feet on center I would forgo overhead storage idea.

He said 4' truss centers!

I am not sure I would even hang a ceiling with 4' centers and a 30' span!