Difficulties With Porches

A few years ago, I was called upon to investigate a complaint filed by a homeowner in a very high end, 55 and older community. The complaint was generated because the homeowner believed that there was mold growing in the crawl space under her home and she was hyper sensitive to air born mold spores.

To paint a better picture, these were all two section homes installed on a masonry (block) crawlspace, on frost protected concrete slabs that were poured 3’ below the surrounding grade.

Once backfilled, the slab will be below the frost line.

The crawl space was properly moisture proofed and the sites were well graded for proper drainage. But the inside of the crawl space was soaking wet even on the nice summer day when I visited.

Notice the wet blocks under the porch area

And sure enough, you could see mold and mildew on the bottom board and in the floor cavity where the access panels were not replaced. The homeowner had a legitimate gripe.


As you know, water is needed to support the growth of mold, so we just needed to find the source of the water. The water source was easy to find. The lawn sprinklers!

Every evening, the automatic lawn sprinklers would slightly overspray the grass and water was landing on the recessed porch decking on the end of the home. The porch was decked with composite material that was installed with just enough of a gap for the water to pass through and collect in the crawl space. The ultimate problem was that the crawl space was constructed around the outside of the porch, instead of just around the living area of the home. So, with every lawn sprinkle, rain or snow that landed water on the decking, water was being introduced into the crawl space.

So, I decided to see what the manufacturers installation instructions say about recessed porches. Most installation manuals have two sentences dedicated to this topic, back somewhere around page 95 of most manuals: “Run the skirting along the perimeter of the homes heated, conditioned space. Do not enclose with skirting areas under recessed entries, porches or decks unless the skirting is of the fully vented type and installed as to allow water to freely flow out from under the home”.  And to complicate matters even further, the ground vapor retarder is not to extend under “recessed entries, decks or porches”.

It would be difficult for an installer is to design a crawl space enclosure-skirting that “allows water to freely flow out from under the home”.

Home sits in a “pit” No way for water to escape.

And even if you did, the homeowner would likely do some landscaping that might act as a dam and trap the water in the crawlspace. Easy to see in these two pictures that any water landing on the decking is going straight into the crawl space.

Water gets captured inside skirting.


As we are seeing more homes being constructed with these decked porches we need to take a harder look at this issue. Running skirting underneath the home is difficult at best. I have run across one example that is well done. In the picture below you can see the porch area is only enclosed with a vinyl lattice that allows any water to escape. And yes, there is a crawlspace wall (skirting) under that front end wall.

Crawlspace under front end wall, behind lattice work.


Maybe some manufacturers have a better idea. But don’t take my word for it, grab an installation manual, turn to the section Complete Exterior Work- Install Skirting. Let me know what you think.