I built a 40 square foot coop over run house for my three girls. We used treated 2x6's on the top portion butted up against each other and secured. The bottom portion is hardware cloth. The top has two isosceles triangles that start off six inches wide and come together at a point after about three feet of steady angle. Hard to explain, but it looks like a three foot long skinny slice of pizza at the top on both sides sealed off with hardware cloth. This is for ventilation. As the coop has "aged" over the last 3 weeks the wood has shrunk by it's standard 1/4 inch. The gaps between the boards that were once butted up tight are now about 1/4 inch to 1/2 gaps. Nothing major barely enough for a fly to walk in between. Where I live, it is not uncommon to get wind chills down to 40 below zero with actual temp in the 10 to 20 below zero range. Last year we had a 56 below zero windchill. Here is my long overdue question.... I plan to cover the "pizza slice" vents to retain heat in the winter time, but...do I need to fill the small gaps between the boards for the frigid winter? I don't want to make it air tight because of the need for venting, but I don't know how "tough" my two RIRs and one Americauna are. Can I use that expandable foam stuff or just let it be? It is up against the house on one side, lattice fence on two sides and exposed on one side. It is also wired with one light fixture. I am already planning on running a heat lamp in the fixture over the winter. Anyone else have this type of bone chilling cold winter? What do you do???? Thanks! Here is a sketch up of the coop I built. Only difference is that there are no vents on the front. only the "pizza slices" on the side.