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Q. We are finding T1-11 at greatly different prices from store to store ($36 at one, $22.50 at another). All claim to be 19/32" and 8" on center. Are there grades of T1-11? Is one company better than another? Should we just purchase the least expensive? p.s. I notice that the exterior surface is only 1/16 inch thick. Can we purchase T1-11 with thicker exterior surface? In other words, how about a T1-11 course?

A. I’m not an expert on T1-11, but I will tell you what I know about it and plywood in general. T1-11 or Texture 1-11 is an exterior grade of plywood with a rough, thus textured, surface. It is often used as siding where economy is important. It is most readily available in 4 x 8 foot sheets with the long edges milled to allow lapping. It can also be purchased in 4 x 9 and 4 x 10 foot sheets from some lumber yards.

There are a variety of styles that you may find. The thicker material that you are looking at usually has grooves cut into the surface every 4 or 8 inches. This helps break up the large flat surface, hides the laps, and gives the “idea” of board and batten siding. The thinner (3/8”) variety is sometimes used with rough 1” x 2” battens nailed up on top to give an even closer resemblance to board and batten. These thinner panels generally do not have grooves cut in them, but sometimes are available with very shallow impressions to mimic the grooves that would be in the thicker plywood. This material is often used in a closed soffit.

Yes, there are different grades of T1-11, but I don’t know what they all are. The differences will relate to the grade of the veneers that are used in the manufacturing process. The better grades will have fewer voids in the interior veneers, and the finish veneer will have only patched defects. The patches in the veneer are football shaped, and having a lot of them should make the panels cheaper. A full service lumber yard with someone that really knows lumber and building products can give you details on what grades are available and how much they cost. The ones that are less frequently used will have to be special ordered and may take a couple of days to get from the mill or distributor.

Plywood in general comes with names like CDX or ABX which tells you what the two outside surfaces are graded and what the adhesive is rated for (X = exterior). All of the grades (A, B, C, etc.) have rules about size and number of defects. There are also differences in plugged or unplugged (the football patches), number of veneers used in the sheet, “solid second layer”, and others. Plywood used for things like cabinet making will have similar grading. Construction grade (as in framing) plywood is rough, has many defects and few veneer layers. Finish plywood will have fewer defects, better patches, and more layers of veneer.

Look closely at the T1-11 that you are seeing and you will no doubt see some differences. If you are only concerned about the looks, and don’t need the structural strength of the plywood, make your decision based on the top veneer. Look at the grooves that are cut in the surface, and if you see a lot of voids in the interior veneers, you may want to look at a different yard.

Remember when you are installing the panels, that you need to use “Z-metal” flashing between the butt joints when the 8, 9, or 10 foot panels are not long enough to cover the wall from bottom to top. Another option is to run a trim band along the wall that you dado a groove into. The groove fits over the top edge to the T1-11 to keep rain water from getting in behind. If you use this method, you will need to put the “Z-metal” flashing on top of the trim band before adding the next set of panels.

 
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