Insulating A Bay Window Sill

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The average home in the U.S. consumes 2 to 3 times more energy than needed, mainly because of insufficient insulation and lack of proper air sealing. These building envelope deficiencies are usually originated during construction. Whether it is a home built many years ago, when energy prices were not a concern, or a house that was just built, you are bound to find the same types of problems -- unless the builder is trained in green building practices and the house is "green" certified.
Besides failing to provide adequate insulation in some key areas like the attic or the basement, the average builder tends to overlook gaps in the envelope left by some architectural features, such as cantilevers, rooms above garages, and bay windows.
Dr. Energy Saver technicians are trained and certified to inspect these overlooked details and locate sources of energy waste in places where most contractors won't think about looking.
In episode 67of the On the Job Series, Larry Janesky, owner and founder of Dr. Energy Saver, walks us through the process of insulating a bay window sill in a relatively new home.
The owner of this house was complaining about drafts and cold air in the room with the bay window. While window manufactures are doing their best to provide more energy-efficient windows, with features such as double pane and low-E glass, it's important that the windows are installed correctly, with proper insulation and air sealing around the frame and sill. Unfortunately, as this video shows, that is not the case in many homes with bay windows.
The window here was sitting on an unsealed and uninsulated sill board, partially exposed to the outside. During the winter, heat was being lost to the outside through the sill and cold air was pouring in through the many gaps around it. A cold window in a warm room creates a convective loop which in turn contributes to even greater discomfort.
For this particular project, Dr. Energy Saver chose to insulate the bay window sill with SilverGlo rigid foam board insulation. SilverGlo is a graphite-infused insulation board. The graphite drives the R-value per inch of the foam up by 24% over conventional foam, by lowering its thermal conductivity. Once the insulation board was cut-to-size, installed, and air sealed, plywood and a 6-inch vinyl skirt board were installed to protect the insulation and give the window assembling a finished look.
Dr. Energy Saver dealers are out every day, all across the US, helping homeowners solve all types of energy problems and make their homes more comfortable, with improvements that pay for themselves by significantly reducing heating and cooling costs.
To learn more about our services, you can watch our other videos, subscribe to the channel for the latest updates, or visit our website to locate a Dr. Energy Saver dealer in your area.

[@garyreed1821]

WOW- its hard to believe that the old windows were not manufactured using this concept- way to go Larry!

[@regionalbasementandcrawlsp3390]

Great job Larry! What an improvement a little insulation can make.

[@Craigthepope]

Looks great. Thanks for the video.

[@cotwold]

Super useful, exactly what i was looking for.

[@mkoschara]

Thank you.

[@MrAquinas1]

Can you do a video on how a good bay window roof should be built?

[@argon805]

thank you, I got a good idea for my customer.

[@chiil034]

Great job Patrick Swayze! I mean - Larry!

[@maryyerke4930]

Can I use this under the case on the outside of my house that holds my gas fireplace? We don’t think the builder insulated

[@joseehumphrey1525]

I have grey powder coming out of the outside of bay window. What is it?

[@carydaniel881]

What is the product you used with the insulation attached to the soffit material

[@mkoschara]

What are the names of the products (Insulated wainscoting, vinyl 6 inch skirtboard) that you are using in the video? I am having a difficult time finding them.

[@Vatos75]

What if the underside of the bay window is vinyl, rather than wood?

[@dr.bobSACC.23107]

What is the name of the insulation with plastic covering called and where can it be purchased? ty

[@dg903]

Why are you using electrical foam?

[@user-cy5xj8ci4d]

You say the name of the silver board but what is the name of the thick foam you mentioned you will use later. I am interested in a one step solution if that could be exposed to the elements. I may have a sprinkler Head that may very slightly get it wet sometimes

[@dr150]

Where can I find the foam board with that brown plastic wainscoting you show off at 3:18?...

[@tvojslauf]

What are you screwing the foam to with those 6” screws?

[@yangmagic0703]

I guess to the bottom of the plywood on top

[@kurtsimmons1587]

My bay window is similar to that. Obviously since this is 9 years old. I would like to know who carries your product. I am tired of sitting in a cold draft myself.

[@JustinPrather]

I'm curious - what are the plastic washers you are using when mounting the foam?

[@dooovde]

They're plastic washers

[@yangmagic0703]

​@@dooovdelol yes. I have a whole bunch of them left over from the roll of foundation wrap I bought

[@SootheSound]

Brilliant. Shame this isn’t flagged by U.K. window installers.

[@irinaburle3750]

What is the name of the insulation with plastic covering called? and where can we purchase this?

[@dr.bobSACC.23107]

Yes, where can that be purchased?

[@lenkaproe]

I have a question, would it be a bad idea to install bay window on a north side of my house (it's a living room). Right now there is a large picture window with double hung narrow windows on either side. What I worry about is the cold north side in winter, but I like the large window sill for seating.

I'm no professional but as this video shows, it's now well insulated. Follow the manufacturers direction and it wouldn't matter if it faces north-east-south-west. I'm here because my 'bay window' is the whole living-room and I have cantilever issues. (in addition that their might not be enough insulation like this video shows)

[@lenkaproe]

+Colin Léger yes, my window and the whole north side is hanging over the foundation by 2 or 3 feet so not much insulation there either. I am not sure if it's a good idea but I will consult a local window installer and see what they say and how much it will cost.

[@LongHuII]

So, please tell us what happened? People also have Bow Windows. some are huge. Look up the video of the New York Sash bow window install. It is insulated. I guess it depends on the house on which one to pick Bow or Bay. I have a problem with the bottom sill and the frame of my bay window. I'm trying to fix it the air just blows right in. Today with vinyl windows and insulation it may be warm enough with triple pane windows to give extra protection against the cold air that creeps in.

[@-8_8-]

Nice job. Looks like it belongs.

[@ballerina6179]

Couldn’t you just spray foam the underside?

[@poetnk]

Very difficult to find any of the products featured in this video through anything but specialty vendors that don't sell cheap to your everyday home owner. Instead of "SilverGlo" look up "SilveRboard", available at your local orange box store. Attach it with prong washers and deck screws. To seal around gaps, look up "Great Stuff". For the skirting, you can likely pick up some good looking vinyl or PVC door jamb / casing / window sill moulding - just make sure you get the exterior stuff. Total cost will run you around $250-300. The largest cost comes from the skirting of all things! IMO the extra plywood isn't really needed if it's in a location that isn't seen. If you were doing a second floor window, then add plywood. IF you use the plywood, always apply a coat of exterior paint to protect and seal it from weather damange (even treated wood will wear if not protected)

[@ballerina6179]

Just found this video. Do you mean that I could use the foam board only without covering it with plywood? Would I just cut the foam board to fit and great stuff seal it with nothing under it? My window is on the first floor and no one would see under it but I’m concerned about the foam board being exposed under the window. (I do see the skirt would protect the sides-but what about the under surface of the window/foam board?)

[@poetnk]

@@ballerina6179 The addition of plywood makes it more durable. If it's in an area where you think the foam could get damaged, then the plywood is crucial, but for most bay window installs which are low to the ground or at ground level, I don't see a reason for plywood. Rodents, etc won't be chewing through that foam - in fact poly foam is used as a rodent block, so if they're not chewing it, weather isn't hitting it, and you're not picking at it - the plywood is not needed. What I will say is - if you're concerned, then set your mind at ease and put plywood. There's really not any harm of going above and beyond minimum requirement if it makes you sleep better.

[@ballerina6179]

@@poetnk thanks! Actually I went out there to investigate under the assumption that my window was exposed and not insulated. I was half right. It’s not insulated but there’s actually vinyl siding under the window and the edges are wrapped with aluminum. I can easily pop out the siding, add the foam board and pop the siding back up. After I get the window leveled that is. It’s an older Marvin bay and it’s dipped down a little so my casement’s reveals are uneven and they won’t come in to lock at the top. It’s always something with homeownership…

[@terraxcell]

I have a garden sprinkler under my bad window. I think I would need something to coat or cover the plywood

[@chriscash5804]

/not to mention there’s no structure to support window lol

[@kevinfarrell2897]

It’s probably cabled. They don’t need bottom braces if they’re cabled, they run down both sides of the center window to the bottom and they’re anchored at the top.