A Backwoods Home Anthology

231The Best of the First Two Years

By H. Skip Thomsen

enerators are notoriously noisy: Ifquiet-as-possible operation is impor-tant to you, then the most importantconsideration in designing your gener-ator shed will be soundproofing.

Probably the best method is to con-struct a small concrete-block building,insulated on the inside with a sound

absorbing rigid foam. If this soundsEke more work and expense than youhad anticipated, or if the aesthetics ofa concrete-block building offend yoursensibilities, a wooden structure canbe made to do nearly as well.

In either case, you will have to pro-vide some sort of positive-flow venti-lation system to keep the inside tem-perature of the building at a reason-

able level. In addition, you will needto make provisions for exhaust and, insome cases, coolant plumbing to getthrough a wall. The building needs tobe large enough for the equipment andfor access all the way around it. (Itwill probably end up about eight-by-eight feet.) Standing head-room wouldbe nice, but it isn’t essential.

Ideally, your generator shed wouldbe located where you cannot hear theengine from anywhere you don’t want

to. But there are other considerationsas well: the cost of running in -thenecessary wire from the generator tothe points of use of the electricity, andaccess for installing and servicing theequipment.

If the location of your shed allows it,the doors should be on the side awayfrom the prevailing weather. This isparticularly important in snow country,

where snow can blow into the doors whenopen and against them when closed.

Your options in constructing a build-ing will depend somewhat on whetheryou have to deal with a local buildinginspector. In most cases, a permit is notrequired if your building is under a certainsize—often 100 square feet, in whichcase an eight-by-eight shed is exempt.

If this exemption does not apply toyour area, a wooden shelter can bebuilt on “skids” and qualify as a tem-porary or movable building, therebyside-stepping the hassles of permits.

Railroad ties work well for the foun-dation of a small building, and theycan qualify as “skids” in the process.

If you prefer the permanence anddurability of concrete and have had noexperience in this area, there are sev-eral good books available for thenovice builder.

In designing your building, you needto consider how the machinery will bemoved into the building initially, andout again, if necessary, for repairs.Doors must be designed to accommo-date not only the size of the equipmentbut the equipment and/or persons nec-essary to move it in and out of thebuilding. Better to have the door open-ing too big than too small.

An easy way to make certain that theopening is big enough is to install twodoors that when open, so as to exposemost of the wall in which they areinstalled. One of the doors can then belatched to the floor and/or the top ofthe door-frame and left closed exceptfor those times when the full openingsize is required.

Railroad tiesWe built the wooden shed for our

CDI diesel generator on a foundationof three railroad ties. The floor con-sisted of four-inch thick planks,spiked together and onto the ties. (Seediagram 1.) From there on up, it wasjust a standard stud-wall building with

How to construct a soundproof generator shed

G

BUILDING

The soundproof generator shed

A Backwoods Home Anthology

232 The Best of the First Two Years

a shed roof and double doors onthe tall side.

We learned much from this building.We insulated every square inch of theinterior with two-inch thick foam, andstill, the whole building seemed toemit a low-pitched rumble when thegenerator was running. The low-fre-quency vibrations of the machinerytelegraphed through the floor into theentire building, and the building itselfacted as a large loudspeaker. Noamount of insulation would complete-ly silence it. But even with the build-ing set up this way, the noise levelwas acceptable in 6our particularinstallation because of the distancebetween the shed and the house.

An isolation padBut what if you cannot isolate the

shed? Isolate the engine/generatorchassis from the walls of the building.How? Mount the equipment on a plat-form

of short ties or concrete, and thebuilding on a perimeter foundation ofties (See diagrams 2 and 3). To makethe noise isolation as effective as pos-sible, the equipment and/or pad mustnot touch the building itself anywhere.

The gap between the foundation orbuilding floor and the pad - can bestuffed with appropriate-sized piecesof foam rubber, or covered with aflexible material like inner-tube rub-ber or heavy-gauge upholstery vinyl.It could also be covered with stapleddown bug screen and used as the floorvent for incoming building-ventilationair. More on that later.

Once the floor is built, whether it isa deck of planks or a perimeter of ties,the building itself is most easily con-structed with basic frame construction(see diagram 4).

Use rigid foam panelsStuds can be laid out on standard

24” centers, or to accommodate what-ever available rigid foam panels youwill use. (Fiberglass insulation is noteffective as sound insulation.)

Full stud-space thickness foampanels or several thinner panels willdo the job. If you use thinner panels,separate them from each other andfrom the outer wall with thin spacers.A floor built of railroad ties and planks

The railroad tie “perimeter foundation”

Cutaway view of equipment pad within “perimeter foundation”

Any added dead air space helps wheninsulating for sound. The innermostfoam panels can be installed right acrossthe studs, thereby eliminating theirability to transmit any noise directly tothe outer-wall sheathing. Use the sameprinciples on the ceiling, too.

Exhaust pipesExhaust pipes get very hot, so it is

essential to route the pipe through thewall of your building in such a way thatit will maintain a safe distance betweenthe pipe and anything combustible.

Make absolutely certain that exhaustpipes are routed well away from anyfuel-lines, fuel pumps or fuel storage!Simply cutting a large enough hole inthe building is one solution, but thatwould effectively sabotage much ofyour sound-proofing.

The answer is to cut a hole that willallow at least six inches of spacebetween the exhaust pipe and anywood. (For- example, a 14” diameterhole for a 2” diameter pipe.)

Cut a piece of galvanized sheetmetal (or aluminum, if you happen to

have any lying around) big enough tocover the hole, then cut a hole in themiddle of the sheet-metal about aninch bigger than the exhaust pipe.With the pipe supported to the wallwith an insulated exhaust hanger(auto-supply item), mount the sheetmetal to the wall so that the pipe iscentered in the hole. Then stuff thegap between the pipe and the holewith fiberglass insulation.

If you feel tempted to route theexhaust pipe out through a hole in thefloor, consider that the operationswhich take place in a generator shedoften involve spilling or leaking offuel and/or oil. It is next to impossibleto clean flammables off a woodenfloor well enough to insure that noserious fire hazard exists.

Coolant plumbing which must berouted out of the shed needs to be iso-lated from the building only to preventengine vibration/noise from beingtransmitted to the building. Simply cutthe hole for the plumbing slightly toobig and pack the space with a resilientmaterial, such as a short length offoam pipe-insulation.

Ventilation is vitalBuilding ventilation is paramount to

insure the health of your generator’sengine. The size and type of enginewill determine the amount of ventila-t ion required, but just about anyengine will eventually overheat in aninadequately-ventilated space. A littleexperimenting with our CDI dieselgenerator dictated that a minimum posi-tive airflow of 1000 cubic feet per minute(CFM) was required to maintain a rea-sonable temperature on a hot day.

Squirrel-cage blowers are hard tobeat for efficiency, especially wherethe size of the unit is a consideration.A fan-type exhaust system wouldrequire such a large opening in thebuilding that any soundproofingwould be rendered ineffective,

A squirrel-cage blower is easy toduct and can discharge through aneight-inch stack. The top of the stackshould be fitted with an elbow facingaway from the prevailing wind to keepout rain and snow. (See diagram 5.)The blower we used in our installationhad a 9½” diameter wheel and wasbelt-driven by a ¼ HP motor.

A Backwoods Home Anthology

233The Best of the First Two Years

The walls on a “perimeter foundation” of railroad ties

The cooling blower

The cooling blower isn’t going to bevery effective without an air inlet thatwill allow as much air into the build-ing as the blower is pumping out. Asimple air inlet is a hole cut in thefloor and covered with a taped-downfurnace-filter element to keep outdust, bugs and other critters.

An alternative is to use the spacebetween the equipment-mounting pad(if used) and the floor. In either case,the opening must be a minimum ofone square foot and there must be anopening of the same size or larger inthe perimeter foundation. A hole inthe floor works better than a hole in awall because the ground under thebuilding absorbs much of the noisethat would otherwise radiate directlyout of the air vent.

A little extra time and effort spent inpreparing a home for your permanentgenerator installation will pay youback generously for years to come.Any mechanical equipment is likely toperform better and longer in a clean,controlled environment, and genera-tors are no exception. And if yourgenerator is your primary powersource, as ours was for 10 years, whynot have the luxury that it be silentfrom your living quarters?

(Parts of this article were excerpted fromMr. Thomsen’s book, More Power to You!,which provides step-by-step instructions forbuilding a high-output electrical systempowered by a diesel engine. It is availablefrom Backwoods Home Magazine.) ∆

A Backwoods Home Anthology

234 The Best of the First Two Years