Large lean to shed plans typically have lower sloped roofs. This is because the single plane of the roof ends up very high if the pitch is too steep. The problem with steeper pitches on larger lean to sheds is that they rise up across the whole shed, being low on one side and high on the other. Because sheds are typically a low cost investment most people want to keep them as economical as possible. This results in using materials that are rated for higher slopes like 4 in 12 and above which makes it easier for the material to keep water out of the shed.

Lean to sheds can be built with lower slope roofs without too much of a cost increase by modifying the application process or a simple change of construction materials. These two main alternatives are to use a low slope metal material or, if asphalt shingles are desired, use of a secondary membrane underneath.

Metal

Many of the standard metal roofing materials sold at home stores and lumber yards are rated for higher slope roof but there are products that are designed to work on lower slopes that can be easily purchased at a roofing supply store. The difference in these materials are the shape of the bends on the panels and the thickness of the panels. Even with these two changes the cost for such a small amount of product is not enough to keep one away from using them to get a lower slope and keep the height to a minimum.

Asphalt

To get regular 3 tab asphalt shingles rated for lower slopes most manufactures recommend installing a waterproof membrane first and then installing the shingles on top of it. These membranes are typically either a self adhering roll material or a mineral surface roll that is essentially the same material as the 3 tab shingles but in a roll form. This "waterproof" layer keeps any water that could be pushed up under the edges of the shingles away from the roof and out of the shed.

Using these two products, or methods, allows the roof to be built down to a slope of 2 or lower, depending on the manufacturer. Most 3 tab shingles are rated for 4 in 12 pitch. By adding the base underlayment the 3 tab shingles can often be installed down to a 2 in 12 pitch. This should be verified with the specific manufacturer before construction begins and definitely before the material is purchased. The application process is done by installing the roll material onto the roof to form a waterproof barrier and then installing the 3 tab shingles on top of it. On a typical shed, 150 square feet or less, this increases the cost of the shed by about $100. Metal roofing materials get their slope rating by the shape of the profile bent into the metal. Like asphalt materials the specific slope rating varies per the manufacturer but it is easy to find a metal material that is rated for 2 in 12 without significantly raising the cost of building the shed.

So whether you want to use metal or asphalt as your lean to shed roofing material it is good to know that there are products and installation processes that will allow you to build the shed with the slope that works best for your site. It is important to consult with your local material supplier to make sure that the specific material you want to use can be used on the lean to shed plan that you have purchased.