There are two ways of adding a structure to the side of a building. It can be done as a lean-to (half structure) that goes parallel to the building and up to the eave, or it can be a complete building at 90 degrees to the existing building. This article applies to the latter option.

When considering attaching an MSS structure at 90 degrees to another building, there are some important considerations to be mindful of before the purchase.

The first is that these buildings are almost always considered high humidity (especially when it is a greenhouse). This means that you will be subjecting that wall to a higher level of moisture. Extra waterproofing should be considered. This high level of humidity should be an extra concern if the intent is to use the warm air as a source of heat for the solid building.

The other thing to bear in mind is the potential snow shedding patterns from the bigger building roof. If the height difference is more than 2’, measures should be implemented to slow the process of shedding snow. Without slowing the rate that the snow comes off the taller building, the force of the impact could be triple or quadruple the weight of the actual snow.

If there is a likelihood of significant snow levels being shed, we recommend reducing the rib spacing of the first 12’ of the building. Going from 4’ to 3’ spacing will increase the strength by 1/3. Going from 3’ to 2’ is a 50% increase in strength. This will give your building the added strength for the impact of shedding snow and the volume that would potentially be on the roof.

The third thing that needs to be considered is how the cover will be fastened to your shelter at the wall. For a stand-alone building, you would be on a ladder or platform off the end but this is not possible if the end hoop is right against the wall.

One option is to have the first hoop about 2’ from the wall and then cover that section with something solid (plywood, sheet metal, Lexan, etc.). This will give you a place to crawl up and secure the cover into the wirelock.

Another option would have you put the first hoop about ½” to 1” from the wall. The wirelock channel would be installed on the underside of that hoop. During the cover installation, you would slide the cover through the gap and then wrap the cover around to the bottom. The wire inserts would be installed from the underside. This option is a little more tricky when doing the double plastic cover. After the cover is installed, the gap can be filled with square foam strips which are available at the building centers. Extra care must be exercised to protect the cover from bolt heads and nuts.

The third option would be to install the structure as per normal but about 1’ from the wall. The covering would be done as usual and once this is complete, the building would be slid up against the wall. This process is a bit risky since the building is not secured to the anchors for a short period. The longer the building is, the more challenging this option is.

The last challenge which needs some attention has to do with the method of ventilation which will be used. Typical ventilation flows through the building. In this scenario, ventilating though the building would also mean that you have to go through the attached building. It can be done, but you would be best to get some additional advice on the process.

If roll-up sides are going to be used, it must be noted that the attached building will interfere with proper airflow.

The challenge with using forced ventilation is “where does the air get into the building. It would be best to create a sketch of the building with thoughts as to what you intend to do. We will use our experience to advise you.

It is important to understand and work through these challenges before you purchase. We are here to advise.