Foam Sill Sealer/Capillary Break
A buildings durability and energy efficiency believe it or not can be greatly affected by some of the smallest and least expensive products out there, and sill sealer is one of these products. As pointed out by James over at Greener Structures, approximately 90% of buildings today do not install a sill sealer or also known as a capillary break.
For a little over $5.00 you can buy a 50′ roll at most hardware stores and even online shops (here). So you may be asking what the big deal is over a sill sealer. Well the product was designed to reduce air infiltration between the top of your foundation wall and sill plate by filling in any gaps or cracks. This product can also be used for slab on grade applications as well where there will be some imperfections in the slab.
Metal stud wall with no sill sealer
As you can see from this image, there is an obvious gap between the concrete slab at the bottom of the new wall being installed. This is going to let in a life time of uncontrolled, unconditioned air that will have to be dealt with by the mechanical equipment, causing it to utilize more energy over the life of the building.
Even though air infiltration is an important aspect of energy efficiency with today’s tight buildings, a sill sealer also acts as a capillary break, stopping moisture from moving from the concrete into the next material. Moisture migration is another big issue that we as building professionals have to take into consideration. So my question to you is, how many of you know that moisture can travel almost 6 miles through concrete? That is a great distance and a whole lot of water that can potentially rot out the wood sill plates or rust the bottom track of metal framed walls. Now you are right that the building codes do not allow for un-treated wood to be in contact with concrete. However pressure treated wood only protects it’s self from rotting out. It does nothing to stop moisture from migrating directly into your band board or floor joists that sit directly on top of that.
Interior wall on concrete slab
Here is a detail that I used on my own home when renovating my basement that I first laid the sill sealer and then attached the pressure treated wood to the concrete slab. Now with the sill sealer, you do not need the pressure treated wood, it just made it easier for me to lay out the walls and take care of some of the irregularities in the floor surface when erecting the interior walls.
Exterior metal stud wall w/ sill sealer
Another small benefit to the sill sealer when it comes to metal wall framing, it will also act as a thermal break between the cold foundation and the steel studs. As I stated, it is a small benefit because the product at most has a value of R-1. However it will provide some resistance between the two highly conductive materials and reduce the chance for condensation to form on the metal studs.
So next time you are working on your next residential or commercial project, make sure you draw that extra thick line and call out the sill sealer/capillary break and get it into you exterior metal stud spec section under “miscellaneous materials”.
Joshua has a degree in architecture and is a LEED Accredited Professional that has worked in the design and construction industry for over 10 years, focusing his efforts on energy efficiency and building science. He has organized multiple events in Ohio to give young designers the opportunity to learn about “green” home design and produce actual projects. He was also a key player in Ohio’s first LEED for Homes Platinum project. Joshua is also a certified Building Analyst through the Building Performance Institute and performs home energy audits, assisting home owners in reducing their energy usage.
