The original set up. This is a very flimsy house and I'm hoping it doesn't blow away or get pulled apart before I come up with a way to strap it down.

It had to come inside. I had hoped I could do it in place, but that would have been a disaster. I did mark where I wanted to cut while it was still up. I wanted to be able to vent high on the wall. I settled on a T shaped cut. In the end I decided to go clear to the bottom so I could really open it up on hot spring days.I could have unraveled the seam. I was afraid that would effect the rest of the seams, so I cut next to the seam.

One thing my searches turned up was to put duct tape on it and cut through the tape. The plastic tears easily otherwise. LOTS of duct tape. I may not have used enough.

Tape it from both sides.

I tried to reinforce any place I thought it would wear.I cut with scissors. The tape puts kind of a sticky residue on your scissors.

I planed to close this vent with industrial strength velcro which comes with adhesive on the back. So now I needed a flap so the velcro would overlap and hook onto the other side. Added more tape, about the width of the velcro.

Poor picture. This is the inside of the top flap. The top flap pulls over the lower velcro, so hopefully sheds water.

I put the hook side of the velcro on the flap and the loop side on the original cut. All of a sudden, picures won't load. I will have to add them later.

Regarding the self adhesive velcro: the internet and DH both thought that adhesive would not be enough. I sewed a reinforcing stitch through the velcro using a large eyed needle and waxed dental floss. Dental floss is so tough, if you need to repair a back pack, a tent, anything that takes a beating, dental floss will do it. Sew your coat buttons on with it, they will never cone off. Sewing through the duct tape and velcro adhesive gummed up the needle. Sewing machine would not have gone through it. If I was going to do this again, I would have used non adhesive velcro and sewn it on webbing on the sewing machine and then taped that in place.

That's a lot of work, Amy. Why add a vent at all? Could you not just unzip the door and vent out through it? Or, are you trying to put a vent somewhere across from the door so that there is air flow through the greenhouse? In a greenhouse that small, keeping plants from baking insie it might be a real chore. Generally, the smaller a greenhouse, the harder it is to get good venting and air flow because heat builds up so rapidly in a smaller greenhouse. The greenhouse effect is real. Even with a larger greenhouse, I keep the doors (and sometimes all 4 vents) open most days, opening them up as soon as the air temperature rises to 33 degrees, assuming it even had dropped below freezing. If we don't drop below freezing, I open the greenhouse as soon as I walk outside early in the morning to let the poultry out. I have 50% shade cloth on the greenhouse year-round. It still can hit 145 degrees in there just an hour or so after sunrise on a winter's day. Running a fan can help promote air flow and push the hot air out of the greenhouse, but I try to restrict running a fan only to the hot weather months, not the cold weather months.

Clearly the solution is a bigger greenhouse. (grin) But, you knew I'd say that, right?

Is the T shape the right choice? It is doing what I expected, but velcro is not as easy to open and close as a zipper. There is no support behind it to help you press the pieces together. I think it will hold up to the wind, unless it gets dirty and can't hold any more. I suspect this is a one season green house, so I don't think the velcro will wear out before the house does.

Yeah, Dawn, cross ventilation was the idea. Last spring I rolled the sides up on the old one so it just protected what was in it from hail. I might be able to do that with this one. This is a smaller greenhouse than the old one, and flimsier. The cover is not as thick. It is not going to hold in heat as well. But it is lower and I think I could throw a couple of frost blankets over it if I chose to. I was hoping to put the citrus in it, but they don't fit. It is time for a permanent greenhouse, a big one. I am trying to talk DH into a lean to type next to the house.

LOL, ain't it the truth!