I purchased a lean-to greenhouse and want to attach it to my shop which is sided with hardiplank siding. The greenhouse frame is powder-coated metal. Can I attach it directly to the hardiplank siding with screws into predrilled holes, then caulk around gaps between metal frame and siding, or is there a better way? What is the best caulk to use?

 

Welcome to the forums! You won't be attaching it directly to the hardiplank, but to the studs and other framing members of your shop. You will only be accessing these members by drilling holes in the hardiplank . Yes, before you drive a screw into the hole, daub it with silicone so the silicone will follow the screw as you drive.

 

You need to go through the Hardiplank and into the studs. The Hardieplank won't hold screws well enough. You may need to place 2X4s flat horizontally between the shed's studs to give you something to screw to.

 

IMO, the best caulk to use is OSI Quad. Sealants used with fiber cement will clearly say so on the tube. they usually say they will meet ASTM-C920. In our area, Lowe's handles Quad.

 

If the greenhouse frame is powder-coated steel, I would avoid directly attaching it to your shop’s hardiplank siding. Without air circulation, moisture will be trapped between the metal and siding, and will eventually cause the framing to rust at a quicker pace and also stain your siding. Greenhouses tend to sweat due to temperature differences between inside and outside, and only aggravates the situation. Unless this is an expensive, high quality greenhouse, cheaper versions usually come w/ poor quality powder coated finishes . . . been there, and done that.

 

Thank you all for your help. After reading your advice, I wonder if it would be best to attach 1X4 to the studs through the siding and THEN attach the greenhouse framing to the 1X4 boards. Then caulk gaps between 1X4 and siding. Would 2X4 be better?

 

Hello Swalt,

First, having owned greenhouses, I have some limited experience with them . . . I've made some mistakes in the past because of not thinking everything through.

I’m not trying to talk you out of directly fastening your greenhouse frame to the your shop’s hardiplank siding as there are things not clear to me. I wanted to point out an issue, and let you evaluate best way to do it since you’re able to see things we don’t know. For example, some greenhouses have polycarbonate film that goes over the exterior frame . . . others have the film or glass on inside of frame. As you probably know, there will be times of the yr. when the dew point is such that this film or glass may be dripping beads of water down the film or glass, and I wouldn’t want to be trapping moisture between the metal frame and siding . . . similar condition when it rains. I didn’t look up where you reside in my earlier post but now see that it is OR. This probably doesn’t apply unless you experience severe weather but here in FL one needs to be mindful of hurricane force winds when building structure . . . for me, I prefer not attaching structures together as they can beat together in high winds . . . without any open space, it will be difficult for you to clean and maintain the exterior side of greenhouse as I’m assuming there is no working room to get between the two structures . . . now whether you will need to get between your shop and greenhouse to clean the greenhouse covering or make repairs is something only you can answer. As you know, polycarbonate film has to be periodically replaced.

I would opt for a stand off from my shop as you’re suggesting in your last post . . . for no other reason, if working w/ steel framing, I wouldn’t want rust stains on my shop’s siding, and most likely it will rust at some point in future . . . you’re weather conditions are likely to be far different than here in FL but rust/corrosion is a major problem in our environment. If this is a small greenhouse able to be moved by you and others, I might consider a quick release design that would allow me to fairly easily separate the buildings if I thought a day would come when needing to paint the shop’s siding or make other repairs to either structure.

Another unknown is whether your shop is sufficiently tall so that it is shading (or partially shading) your greenhouse depending on angle of sun which will change over the course of a yr. Again, I’m not in a position to know what your planning to grow, or whether shade would be an advantage or disadvantage in what you're trying to do. A greenhouse environment presents a number of challenges that I’ve not encountered before . . . consistency of sunlight within the greenhouse makes it easier to set-up water regimes whereas they may need to be altered if some part is shaded as temperature and light effect how the plants respond and can create conditions that promote fungal problems if soil for one group of plants remains wetter than others . . . just give it some thought.

Good luck.

 

If you want to have a flat surface to attach to, you would have to cut out the siding in order to attach any 1x4 trim. Nailing any trim on TOP of the siding would be pretty hokey. Of course I guess that's the way they usually do it in some parts of the country. (slam-bam tract housing)

And what you would probably want to use is a 4/4 x 4, which is a full 1" thick. You could use hardie trim (cement) Miratec (borate treated fiber) SmartTrim (LP) or probably a few other products that would be similar. Ideally you would have backing in the wall to nail this trim to (sides especially), but you could also attach it to your sheathing, provided it is a minimum of 7/16" ply/osb. You would install a drip cap over the top trim. Ideally, you would also have a head flashing for your greenhouse.