Outdoor (Insulated) Generator Box Build

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Blog entry by MayflowerDescendant posted 11-13-2010 03:38 AM 80359 reads 1 time favorited 14 comments Add to Favorites Watch

When my wife and I relocated from Southern Ontario to the West Coast of British Columbia, we (by-and-large) left cold and snowy winters behind us. While it was easy to adjust to a more temperate, albeit wetter, climate, the occasional coastal windstorm (with winds up to 100 km’s/hour or 60 mph) can easily disrupt your hydro / power supply. Even though the power lines in our area are all underground, we are “fed” from areas where the power lines are above ground. Trees / limbs come down, power is cut. And, while we have experienced some minor earthquakes over the years, if we do experience a significant one, you have to anticipate some major (and prolonged) power outages. One solution: a decent-size generator. Big enough to power household essentials – fridge, freezer, microwave, kettle, tv, radios, heater, few lights, etc. – in the event of a power failure.

Once one has decided to implement this solution, you walk through the related issues of portability versus permanent / stationary (outdoor) installation, method of feeding power into your home, some form of protection from the weather (assuming it is being stored outside), and security (so it cannot easily “disappear” on you). In response to these issues, I designed an outdoor / insulated generator box. What follows is a detailed progression of the build, from basic box construction to final installation.

The size of the box was dictated by the size of the generator – mine includes handlebars and pneumatic tires – and the need / desire to have plenty of clearance top to bottom, side to side and back to front. The box (including base-mounted drip edges) measures 72-inches long, 44-inches deep, 52-inches tall at the back, and 42-inches tall at the front. The box frame (and various doors) is constructed of 2×2, covered by 1/2 –inch exterior plywood. All interior, non-visible surfaces (2×2 and ply) have two coats of primer. The walls and lid are insulated with 1½-inch solid insulation, before being vapour-barriered and skinned with ¼-inch ply. That ¼-inch ply has two coats of primer on the insulated side (non-visible surface) and three coats of exterior, semi-gloss Varathane facing the visible / interior of the box. Same goes for any 2×2 surfaces. The exterior of the box has two coats of primer and two coats of paint (matching the trim of my house).

The base / floor that the box sits on is ¾-inch pressure treated plywood, screwed to a 2×4 pressure-treated frame with multiple cross-members. Each section of the base is insulated by 2-inch solid insulation, vapour barriered and covered with ½-inch exterior sheathing. Wrapped around the base and box is a drip-edge overhang cut from pressure-treated 2×4’s and bevelled appropriately at the corners. All pressure-treated base and overhang surfaces have 4 coats of exterior, semi-gloss Varathane.

The left-hand side of the box features a fully removable door with an integrated vent. The idea here is … in reasonably good weather (when I’m simply running the generator – on a periodic basis – to ensure it will start / run when required), I can fully remove the door and let all the air in I want. In an absolute monsoon situation, I can leave the door secured, keeping the interior of the box dry, while allowing adequate air supply into the box via the 14-inch by 20-inch louvered and screened vent.

The front door is hinged on the left and swings out a full 90-degrees to allow full access to the generator control / start panel. If you are wondering how I start the generator, it is a key start model – no pulling a hefty chord (and dislocating my shoulder). Once started, I partially close the door, sheltering the control panel from the elements but allowing more airflow (versus if I closed it completely). The door and lid overhangs prevent the elements from entering the box.

The rear door unbolts and swings out, directing and allowing the exhaust to escape out the back of the box. Notice (in the final installation pictures) that the door has a sheet of galvanized metal over top the wood to take the exhaust blast / heat from the generator’s exhaust. The exhaust is warm (not really hot), but not enough to heat the metal so it becomes scorched or to cause concerns of catching on fire. Between all the surrounding space, airflow and means of exhaust, I have had no issues with heat / gas / fume build-up.

The lid is sloped for water runoff. It is hinged across the back to allow for full opening. This allows for easy generator inspection and fueling from the top. At the moment, the lid can be held open by hand or a length of 2×2. Given the lid’s weight, I am in the process of securing some lift assists (spring or gas-loaded) to make it easier and hands-free. As a matter of practice, when the generator is running, I do prop the lid up slightly (say, 2-inches or so) to help with airflow and heat dissipation.

Other features of the box include: overhangs above the doors and vents, and drip edges at the bottom of the front door and around the base of the unit. These serve to shed water away and prevent it from entering the box. Aluminum screened vents near the top of the back and right hand side wall. These serve to both enhance air flow through the unit while running but also ensure adequate airflow when the box is closed up. If we happen to experience some extreme cold conditions, I have insulated vent covers ready to insert from the inside.

All doors, vents, and the lid are also wrapped in waterproof gasket material of varying thicknesses and widths, depending on location. The box consumed over 500 stainless steel screws, while the pressure-treated base / floor took about 80 coated deck screws. Most (if not all) hardware is Stanley Exterior / Lifespan or Weathergard series, mounted using stainless steel screws (versus what they come with). The (blue) padlocks are Lee Valley’s “weather-resistant” locks (product number 00F25.01). Most exterior, mating surfaces (e.g. drip edges ./ overhangs) are caulked with either beige or clear silicone.

I did not track the number of hours I put into this project over the 14-months or so that it sat in the middle of my shop. I worked on it between various other projects. The entire unit has to weigh several hundred pounds. To move and install it outside, I had to break it down to the base, 4 walls and lid, and re-assemble in its final resting place. After ensuring it was well-seated into a bed of crushed gravel, level and aligned with the power feed into my crawlspace, the generator was introduced to its new home.

The Effect of Insulating the Box

After installation, we experience several weeks of unusually warm weather here. With the box closed up, I sat one Min-Max thermometer (Lee Valley product number AB803) on the South-facing lid surface and another Min-Max thermometer inside the box. The lid SURFACE temperature hit 50 degrees Celsius (or 120 degrees Fahrenheit), in the mid-afternoon sun. That same (clear) night, the lid surface temperature dropped to 18 degrees C (or 64 degrees F).

Inside the box, the temperature hit a maximum of 33 degrees C (or 92 degrees F), that afternoon. It fell to 26 degrees C (or 74 degrees F) that night.

These results speak to the performance of the insulation and ventilation the box design entails – the interior of the box was approximately 17 degrees C (or 28 degrees F) cooler during the day and 8 degrees C (or 10 degrees F) warmer at night – than the exterior surface temperature of the box.

So far, we have yet to experience any really cold Fall temperatures to do another set of readings. On the West Coast, we only get a few sub-zero days / nights in the average Winter. Temporarily, closing up the vents on those nights should more than ensure the interior of the box / generator does not fall below freezing.

Mission accomplished!

-- Glen - Vancouver, British Columbia, Canada

14 comments so far

View TopamaxSurvivor's profile


24556 posts in 5130 days

#1 posted 11-13-2010 04:18 AM

Looks like you did a real nice job. Why are you worried about the generator getting below freezing?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View MayflowerDescendant's profile


414 posts in 4241 days

#2 posted 11-13-2010 06:32 AM

Topamax … No big, big worry about the colder temps / freezing … other than … it can’t hurt to be insulated and snug. After all, when you need a generator, you need a generator. Anything that increases the chances that it will start (when needed) is good in my book. P.S. I run it (at least an hour) every weekend, just to keep everything working and passing fresh fuel through it.

-- Glen - Vancouver, British Columbia, Canada

View NBeener's profile


4816 posts in 4629 days

#3 posted 11-13-2010 07:32 AM

To my way of thinking, over-engineering is a great place to start ;-)

It’s clear that you took your time, anticipated the challenges, and really set about nailing them down.

Beautiful job. May you never need to use it ;-)

-- -- Neil

View ND2ELK's profile


13494 posts in 5229 days

#4 posted 11-13-2010 08:48 AM

That is quite the box. Very well done. Thanks for posting.

God Bless

-- Mc Bridge Cabinets, Iowa

View TopamaxSurvivor's profile


24556 posts in 5130 days

#5 posted 11-13-2010 09:12 AM

Just curious, i usually ask to many questions, but once in a while I learn something ;-)) If you can get some stuff called “Seafoam”, similar to “Sta-bil” to put in the gas, it will run better and the fuel can set almost indefinitely. Definitely over a year. Mechanic i know said it has fixed engines he couldn’t quite get going right.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Pawky's profile


278 posts in 4258 days

#6 posted 11-13-2010 09:25 AM

I will second what topamax said about the seafoam. A motorcycle forum I am on has a ton of people that rave about it and well, since trying it I have to agree. I now use it on all my vehicles and really anything that takes gas/oil. I’ve used it on my lawnmower, weedwacker, older truck, middle aged jeep, new motorcycle, dad’s RV, etc… Like was mentioned as well, I’ve seen it turn an engine go from barely working to running very well. It’s super simple to use and can be used in the gas, oil, or gas/oil mixtures.

Also, the generator box looks like it is greatly built, well done :)

View TopamaxSurvivor's profile


24556 posts in 5130 days

#7 posted 11-13-2010 09:43 AM

And diesel too :-))

Mayflower, are you planning to run the gen with the top open?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View MayflowerDescendant's profile


414 posts in 4241 days

#8 posted 11-13-2010 10:27 AM

Topamax … Yes. As I state in the blog, “As a matter of practice, when the generator is running, I do prop the lid up slightly (say, 2-inches or so) to help with airflow and heat dissipation.” It’s not absolutely necessary – I’ve run it with the lid fully propped open, a little bit open and closed – and it makes little difference from a heat build-up standpoint. There is plenty of clearance between the top of the generator and the lid, along with good airflow from left to right. Remember, the left hand side door is removed, both the front and back (exhaust) doors are open when running, and there are upper back and right hand side vents. Before I even tested it with the generator, I sat in the enclosed box (on one of the hottest days in August). With just the vents (no doors / lid open), there was great airflow through the box. Where I live, we enjoy a steady breeze flowing West to East, right down between the houses, feeding the box with air and dissipating the exhaust.

-- Glen - Vancouver, British Columbia, Canada

View TopamaxSurvivor's profile


24556 posts in 5130 days

#9 posted 11-13-2010 11:23 AM

I was thnking about long term runs, not just the 1 hour. Guess it is getting plenty for an hour, it wouldn’t matter. Nice that you uhave natural ventilation for it ;-))

You know when the big one comes it will be the Jaun de Fuca plate breaking off and the continental shelf will drop about 3.5 meters, don’t you? It will be a #10 or higher. Puget sound will drop up to 60 feet and the tsunami filling it back up will be as high as 60 feet. Mt Rainer will probably lose another 200 feet off the top. When the last one hit in Jan 1698 +/- Rainier is thought to have been 16,000 feet high. 2000 feet caved in and melted. The mud flows went down all he major river valleys. Down town Puyallup will have 45 minutes warning before 30 foot high wall of mud comes through at 45 mph. 90% of the bridges on the I-5 corridor will be down. What I am saying is store a lot of fuel!!

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Doug Scott's profile

Doug Scott

67 posts in 4415 days

#10 posted 11-14-2010 05:21 AM

After looking at your cover for your generator , it put mine to shame. but my make shift cover didn’t take me hours of time or any money out of pocket. Live in Western Michigan 50 miles west of lake Michigan and we get lots of wind and snow and my generator has never failed to start over the 10 years It’s been stored where it is. Stacked up 4 rows of cement blocks on each side , both sides have the blocks so that it get ventilation and exhaust goes out the other side , with a metal roof of 2” insulation and a removable door in front, The roof over hangs the doors to prevent the snow and rain from getting in. AND it’s not locked up , It’s in the back of the garage so no one can see it . SORRY NO PHOTO, Yet !

-- Doug, Michigan,

View Karson's profile


35300 posts in 5855 days

#11 posted 11-14-2010 07:17 AM

Nice job on the build. A very useful adition to the generator.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View prez's profile


376 posts in 4866 days

#12 posted 02-10-2011 11:32 PM

Another plus for the insulation is that it is a great noise muffler and the neighbours don’t complain about the noise of the generator! Right Glen?? I know mine will get on your nerves if left on for hours on end…..luckily, that hasn’t happened yet! May have to see about a box like yours…”next winters project”!

-- George..." I love the smell of a workshop in the morning!"

View Bertha's profile


13635 posts in 4148 days

#13 posted 02-10-2011 11:45 PM

That thing could double as a safe. I enjoyed looking at it. Makes me wonder how much I paid for the plastic cover over my permanently mounted standy-by.

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View MrZ2u's profile


20 posts in 2667 days

#14 posted 03-02-2021 03:36 PM

Curious the state of things 10 yrs later?

Down here in Central Texas (well, all of Texas really) we are a week or so on the other side of the Snowpocalypse and generators are selling like ice tea in hell right now.

I am looking to make a more permanent home for it like you have there. I primarily want the “garage” for the genny but I am thinking about the insulation for noise abaitment. Down here it hot most of the time so interior temps and air flow concern me when it comes to an air-cooled engine. Do you have any data on temps inside on extended runs in hot and cold months?

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