Redwood No Longer an Option for Hot Tub Builders

 Redwood No Longer an Option for Quality Hot Tub Manufacturers

Few species of wood, other than “Old Growth”, have enough natural rot resistance to be acceptable for use in top quality wooden hot tubs.

“Old Growth Forests” as defined by Wikipedia, are “areas of forests that have attained great age and exhibit unique biological features.”

Old Growth Forests are also commonly referred to as Ancient Forests, Virgin Forests,
Primary Forests and Ancient Woodlands.

Forests that have not attained great age due to severe disruptions, such as clear-cut logging or wild fires, are referred to as Regenerated or Second Growth Forests.

Forests remain classified as “Regenerated” for a very long period of time and until all of the effects of the severe disruption are no longer evident. Depending on the forest, this may take anywhere from as little as a century or as long as several millennia.

As their name states, Old Growth trees grow very slowly over long periods of time. One significant reason for their slow growth is the struggle for sunlight being blocked by neighboring trees.

Slow growth can be seen and measured by looking at the growth rings of the tree, some of which can have up to 50 rings per inch, indicating that it took the tree 50 years to add 1 inch of girth. Slow growing species of wood with tighter growth rings have proven to be much more rot resistant than faster growing trees with wider growth rings.
timeline3The space between trees and the sunlight conditions for Regenerated and Second-Growth Forests are much more conducive to fast growth and in an ideal atmosphere, second growth trees can have as few as 3 growth rings per inch.

In 1996 one of the largest lumber companies in the world, The Pacific Lumber Company, entered into an agreement with the US government and the State of California known as the Headwaters Forest Act.

This agreement all but ended all large scale commercial harvesting of Old Growth Forests in general and Old Growth Redwood Forests in particular. What remains is a very small supply of “reclaimed” old growth redwood and a minuscule amount of old growth redwood being produced by some very small, privately owned mills.

The vast majority of redwood on the market today is regenerated or second-growth and is completely unacceptable for use in any hot tub and even more so for a quality Roberts Hot Tub.

The image below shows the difference between an Old Growth Western Red Cedar Hot Tub Stave and a Second Growth Redwood Hot Tub Stave.

The image to the left shows one of our typical western red cedar staves from Roberts Hot Tubs. There’s up to twenty (20) growth rings per inch.

This image on the left shows a redwood stave from one of our hot tub competitors. As you can see, there’s only two or three (2-3) growth rings per inch.

                                                            There’s No Substitute for Quality

Round Wooden Hot Tub Assembly Instructions

Unlike others, our hot tubs are manufactured with perfect computerized accuracy and require absolutely no on-site milling or cutting of the final stave. Each tub fits together perfectly and assembles quite easily in an average time of less than 1 hour.

*Please note, the following assembly procedure is a slightly condensed version of the actual included instructions. Various size hot tubs of various types of wood may have slightly different instructions and ONLY the actual instructions included with the hot tub should be followed.

Important Note – Please read through the entire procedure carefully before beginning the first step.

Round Wooden Hot Tub Assembly Instructions

To assure a long-lived and structurally safe tub, a properly designed foundation is essential! To withstand the weight of the tub and water we recommend a minimum 4″ thick reinforced concrete pad. If you have any questions please contact us for proper and adequate site preparation.

Step 1: Installing the Suctions

Place the chine joists on the concrete pad so that they are 5½” tall and arranged as shown in Figure 1. Check the chine joists with a level and make any necessary adjustments. Next, put the three dowel pins in one half of the bottom and place the bottom-half on top of the chine joists. Be sure the side of the bottom that is nicely sanded is the side that faces up.

If you plan to put one or two suctions in the floor of the tub, it is easiest done before the tub is assembled. If BOTH suctions are being installed in the floor (Figure 1), they should be separated by at least 3′.

Be sure the location of the suctions does not interfere with the chine joists and be sure the holes are drilled wholly on one board. The suctions require a 2½” hole. If you use a hole saw you will have to drill from both sides of the board. This will eliminate any tear out from the bottom side.

To install the suctions, first slide the gasket on to the through-wall fitting. Then apply a generous bead of silicon sealant to the end of male threads of the through-wall. DO NOT apply silicone to the flange or the gasket. Next, slip the male threaded through-wall fitting into one of the holes.

Screw the female threaded nut onto the suction body. Be careful not to over tighten the nut; snug hand tightening should suffice. (If the nut is screwed onto the through-wall too tightly, the swelling of the wood when it gets saturated may crack the flange, leading to leakage.) Repeat these assembly steps for the other suction. At this point it is advisable to complete any other plumbing that occurs underneath the tub.


STEP 2: Assembling the Base

Put the other half of the bottom on the chine joists and then slide the two bottom halves together, pushing them together as tightly as possible. Note that the bottom boards are placed perpendicular to the chine joists as shown in Figure 1.

After the bottom is in place the two plywood strips supplied with the hot tub must be screwed down across the seam of the bottom halves. Place the strips about 3″ in from either end of the perimeter of the tub. Use four 1″ screws to secure each strip. Remove these strips after the hot tub is fully assembled.

*Please Note: Failure to use the plywood strips will cause trouble in later procedures.

STEP 3: Fitting the Staves to the Base

Each stave must be properly positioned between the alignment notches located around the perimeter of the bottom. You will note that in Figure 2, the side of the stave that has a tongue is centered directly on the alignment notch. The side of the stave that has a groove does not line up perfectly on center of the alignment notch.

All the staves go on in this fashion. There will be gaps between every stave put on the tub. Do not worry about these gaps and do not drive the staves on with a mallet. The staves may be lightly tapped on with enough force to keep them from falling off. Once all of the staves are on, the tub is ready for the bottom band.












STEP 4: Applying and Tightening the Bands

Figure 3 shows the bottom band at 42 5/8″ down from the top. Drop the band over the top, lower it into position and tension the nuts a little so that the band does not fall off. Go around the tub with a tape measure and check the height of the band. Once the band is properly leveled, you may begin to tighten the band.

This process is best performed by two people. While one person tightens the bands, the other person strikes the band with a soft face mallet. A metal mallet will also work but do not strike the band directly. Use a block of wood as a buffer.

The stave boards should be driven on slowly. Start by gently pounding on each stave all the way around the tub. Make another revolution around the tub, pounding a little harder. And then another revolution pounding harder.

The object is to drive the boards on evenly all around the tub. It usually takes 4 or 5 times around the tub to accomplish this. The bottom band requires a lot of tension. Tighten the bottom band nuts to the point where you meet a lot of resistance.

Try to avoid stripping the nuts from over tightening. After the first band is completely installed, put the second band on 23¼” down from the top and tighten the nuts. The top band is placed 4″ down from the top. This band does not require as much tension as the bottom band.











STEP 5: Finishing the Tank Top Rim

Go around the top rim of the tank with either an electric hand plane or a belt sander to level the top edge. If you use an electric plane, it’s a good idea to smooth the planed surface after-wards with a belt sander. Finally, round off the inside and outside edges of the top rim, using a router with a quarter-round-over bit.

Installing the Bench

Follow the procedure outlined below to install the bench in the tub. All necessary parts have been provided, including hardware. Tools required include a variable speed electric drill, a #2 Phillips head driver bit, a #10 pilot bit, a measuring tape, and a straightedge.

1. Decide how high the bench should be mounted in the tub. Factory-made tubs are assembled with the top of the bench 16½” above the floor of the tub, but the bench can be mounted higher or lower to suit you.

2. Now you can determine where the 2 x 4 bench supports should be attached to the tub’s staves. Measure up from the floor of the tub and make a mark 1½” below the desired bench height. Make sure this mark is centered on a stave.

3. Holding one end of a support against this mark, make a mark on the tank where the other end falls. Using this mark as a horizontal guide, measure up the from the floor the same distance (1½” below the desired bench height) and make a height mark for the other end of the support.

NOTE – To ensure that the screws will not go completely through the side of the tank, these holes MUST be drilled about 2-1/4″ from the longer end of the beveled bench support and perpendicular to the beveled edge (i.e., at a 45º angle with respect to the outer surface of the support, and angled toward the bevel.

4. Note that both ends of the support have beveled sides, which go against the staves. Using a #10 pilot bit, drill two holes through each end of the support for the screws that will attach the support to the tank. These holes should be about ¾” from the top and bottom edges of the support.

5. Using a power drill and the screws provided, attach the first support to the tub wall.

6. Select another support and repeat steps 3, 4, and 5. Then repeat this procedure for the other two supports.

7. Place one bench section on top of the bench supports, centering it where two supports meet, as shown in the illustration.

8. Insert two of the splines provided into the slot in one end of the bench section and slip the end of the next bench section over the protruding edges of the two splines.

9. Repeat step 8 until all the sections are laid out.

10. Center the assembled bench so that each of its corners is equidistant from the tub wall.

11. Use a straightedge to mark the center-line of each bench support on the bench sections it supports.

12. Using the #10 pilot drill you used before, make holes along the line you just drew. The drilled holes should be near the splines but take care not to drill through any of the splines, a make sure that each bench section is attached by two screws.

13. Use your electric drill to drive the screws provided through the pilot holes and into the supports, countersinking them about ¼”.fig-bnchr


*One hour average assembly time is for just the hot tub itself, and does not include carrying parts to assembly location or installing the complete system.

Installation Preparation & Services

plan-prepare-execute1Proper hot tub installation preparation requires that you arrange for the following three items prior to installation.

  1. Proper Electrical Circuit
  2. Proper Sized Gas Line
  3. Cement Pads/Foundations for Hot Tub & Equipment


Electrical Requirements

The standard electrical requirement for our complete hot tub system is a 240 volt, 20 amp circuit including a white neutral wire and a green insulated ground wire that is required by code.

Checking_voltageNational electrical code requires that the wiring be in a metal conduit and must have a disconnect switch within visible distance from the pump. Local codes may vary by city and state.

A 30 amp circuit is required for our standard/basic complete electric hot tub system with a 5.5kw heater, but you’ll need to add an additional 50 amp circuit if you upgraded your tub heater from 5.5kw to11kws.

We recommend that you check with a local electrician to make sure that your equipment meets the proper amp requirements prior to adding additional jets, pumps or accessories such as an air bubble system.

Gas Requirements

Our basic gas powered hot tub system includes a 100k BTU heater and requires a gas line of sufficient size. Upgrading to a larger heater might require a larger gas line and it’s prudent to check with a local gas professional prior to upgrading. Please remember that gas lines should only be sized and installed by licensed professionals.

Cement Pad/Foundation Requirements for Tub & Equipment

concrete_padAs we mentioned earlier in the “Locating Your Tub and Equipment” section, you will need a concrete pad or foundations for the hot tub and a concrete pad or foundation for the hot tub equipment.

Our basic equipment package requires a concrete pad of 24″ by 54″, although it can be squeezed into a slightly smaller area if absolutely necessary.

If you must use a slightly smaller area, we recommend that you wait until you have the equipment in your possession prior to pouring your concrete pad.

The hot tub itself also requires a concrete pad or foundation to sit on. For stability and settling purposes, the tub itself should sit on a single solid concrete surface. Everything settles over time and just like the concrete slab under most homes, concrete settles but remains flat.

install6Tubs have successfully been installed on blocks, in gravel or on pier block foundations, but the settling process is much more likely to be uneven.

An uneven settling process can concentrate the stress on a single area of the tub causing premature cracks and leaks.

The minimum thickness safety requirement for a basic hot tub pad is 4″ thick reinforced concrete with a diameter of 6″ less than the diameter of the bottom of the tub. Therefore, a 5′ round straight sided wood hot tub would require a 4′ 6″ square pad.

The type of ground underneath the pad should be stable as well. If the soil has a propensity for expanding and contracting due to extreme freezing or scorching temperatures, you may be required to add concrete footings to stabilize the pad. Checking with a local contractor is an easy way to find out whether you need footings or not.

install3Sunken or semi-buried tubs have also become very popular and they are much easier to get in and out of.

A wooden hot tub easily be installed below grade with a few minor adjustments.

You will need to dig a pit large enough to accommodate the size of the concrete pad and build a retaining wall around the pad to keep excess dirt and debris from eroding and coming into contact with the tub itself. The retaining wall should be made of concrete, concrete block or ‘ground contact’ rated pressure treated wood.

Please make sure that you leave a minimum clearance of 12″, preferred clearance is 24″-36″, around the entire tub; a 5′ diameter tub requires a 7′ wide hole. This clearance allows you to pre-assemble the tub above the pit and then lower it into place.

Tub assembly requires a minimum of 24″ of total clearance around it for proper construction. You may also want to consider adding a sump pump in the pit depending on drainage and ground water.

hottub20Installing a hot tub on or in an existing deck is also quite popular, but most decks aren’t constructed to accommodate the weight of hot tub filled with water.

An average hot tub filled with water weighs in excess of 5000 lbs. before you and your friends jump in and we strongly advise hot tub owners considering tub installations on existing decking to check with a licensed engineer prior to beginning tub installation.

Hot Tub Location Guidelines

locationLocationThe most important part of any hot tub installation is proper planning and the first two steps of the planning process are deciding the ideal location for your hot tub and your hot tub equipment.

The vast majority of our customers prefer to install their hot tubs outdoors, but our tubs can be installed just as easily inside your home as out.

Our Hot Tub Photo Gallery is full of unique location ideas, creative inspiration and great examples of where other hot tub owners have located their hot tubs.

Location of Your Hot Tub

roundtub56Roberts Hot Tubs has been in business for almost 40 years and history has taught us that your tub will be used and enjoyed more often the closer it is to your house or bedroom.

Installing your hot tub on or submerged in an existing outdoor deck is ideal for many hot tub owners, but please be aware that most decks are not designed to support the weight of a hot tub filled with water.

We strongly advise that all hot tub owners considering tub installations on existing decking check with a licensed engineer prior to beginning tub installation. Please remember that the average hot tub filled with water weighs in excess of 5000 lbs. before you and your friends jump in!

hottub37Outdoor Installation Locations

Depending on where you live and the size of your yard, there can be an endless number of ways and places to install an outdoor tub.

That said, there are certain health and safety restrictions that will influence where your tub can be located.

1. For stability and settling purposes, the tub itself must sit on a single solid concrete surface. Everything settles over time and just like the concrete slab under most homes, concrete settles but remains flat.

If your tub was set in gravel or on piers, the settling process could easily be uneven. This puts undue stress on a single area of the tub and can cause cracks and leaks.

2. The tub rests on joists that we provide rather than making direct contact with the concrete pad. The size of the concrete pad can be 6 inches smaller than the tub’s diameter, so a 6′ diameter tub only requires a 5′ 6″‘ square concrete pad.

Saving 6″ on the pad means pouring less concrete as well as insuring that the pad won’t protrude any farther out than it absolutely has to. The typical thickness of the concrete pad should be 3-1/2″ with reinforcement wire for extra strength.

3. The type of ground underneath the pad should be stable as well. If the soil has a propensity for expanding and contracting due to extreme temperatures, you may be required to add concrete footings to stabilize the pad. Checking with a local contractor is an easy way to find out whether you need footings or not.

4. The overall height of the tub is also a consideration. A 4′ tall standard hot tub will stand a total of 49-3/4″ off the top of the concrete pad with the exception of our European Timber Tubs which stand 50-5/8″ high.

Based on this height, you may want to consider sinking part of the tub into the ground. Sunken tubs are extremely popular and are much easier to get in and out of.

In order to safely “sink” your tub, you will need to dig/construct a tub pit. The pit should have retaining walls to keep any excess dirt from eroding and coming into contact with the tub itself.

We recommend that there be a minimum 12″ clearance between the walls of the pit and the tub itself; a 5′ diameter tub will need a 7′ diameter pit. Another thing to keep in mind is that the tub will require a minimum of 24″, preferably 36″, of clearance around the entire tub. This will allow the tub to be assembled above the pit and then lowered down.

Indoor Installation Locations

6Indoor installations aren’t that much different than outdoor installations, but they do require a few extra considerations.

The main consideration with indoor installations is moisture and the effect it has on other areas of your home.

1. Moisture – It’s common practice to use hot tub insulated covers on outdoor hot tubs and the same is true with indoor hot tubs. Insulating covers save time, money and energy inside and outside, but quite a bit of steam is released when you take off an indoor cover.

Steam doesn’t play well with other interior sections of your house, so you need to make sure that the room your tub is located in has good air flow and very good ventilation.

2. Chemicals – Along with the steam factor, there’s also the issue of sanitation and the use of hot tub chemicals. Hot tubs that are used regularly need to be sanitized with chlorine, bromine or a non-chlorine shock treatment in combination with smaller amounts of chlorine or bromine.

These sanitizers can produce foul smelling odors that go well beyond the room your hot tub is located in. Ozone is another form of sanitizer that should not be used indoors. High concentrations of ozone can accumulate in the room that your tub is located in and cause severe throat irritations as well as corrode plastic and printed electronic circuitry.

The best sanitizer to use indoors is an ionizer in combination with periodic non-chlorine shock treatments. One maintenance advantage to indoor installations is that less dirt, debris and pollen get into your tub which might save you a few dollars per year on sanitizers.

3. Leaks – The other big moisture consideration is “leaks.” As much as we hate to admit it, the possibility of an indoor hot tub cracking, breaking or leaking does exist and the odds increase as the tub gets older.

After years and years of use, a seal or gasket could wear out and cause anything from a small drip to a giant flood. We strongly recommend that indoor hot tub owners take special precautions by installing a waterproof flooring membrane and floor drain in the room that the tub and equipment are located in.

If the tub equipment is installed in a garage or basement, it’s a very good idea to set the equipment in a waterproof pan with a drain to insure that any possible leaks won’t damage surrounding items.

Equipment Location & Layout

Equipment Location & Layout


After you’ve received your hot tub, the next consideration is locating the equipment.  With our standard hot tub system the equipment will take up an area up to 3′ wide by 5′ long.

The equipment can be squeezed into a smaller area, but know that this can make basic maintenance and any future repairs a bit more difficult.

As for where to locate the equipment, the possibilities are great. National code (your local code may differ) requires the equipment to be located at least 5′ from the tub unless separated by a permanent solid barrier.

Most people locate it much further than that. One of the advantages to a hot tub over a portable, or self contained spa is that you’re not sitting on top of the equipment having to listen to it while in the tub. Where you locate the equipment is up to you, but please keep the following important information in mind:

  • If located more than 50′ from the tub, the pump and piping should be upsized so as not to experience pressure loss in the jets from greater friction loss.
  • If the heater is located more than 5′ below the water level of the tub, a simple adjustment to the heater will need to be made. If located more than 10′ below the tub, a special flow switch will need to be installed to prevent the heater from operating when the pump turns off.
  • If the pump is located above the tubs water level, it could loose it’s prime causing water circulation to stop and possible pump damage to occur (please let us know if this is how you’re installing your pump so we can provide a different pump and valves to help prevent this).
  • If the equipment is more than 20′ from the tub it may be advantageous to insulate the pipes to help lower heating costs.
  • With a long pipe run there tends to be quite a bit of water in the pipes. If the pump hasn’t run in a few hours, and you get in the tub and turn on the jets, all of that ‘cooled’ water will need to be flushed out (against your back) before hot water starts bubbling from the jets. Remembering though to turn on the pump 5 minutes or so before getting in the tub easily overcomes this.
  • A gas heater requires a certain amount of clearance above it for safe and proper operation. Our standard gas heater needs a minimum of 61″ of total vertical space for installation (25″ tall heater plus 36″ of clearance).
  • The filter in our standard hot tub system requires a minimum vertical height of 50″ for basic maintenance (smaller and shorter filters are optionally available).

Helpful Photos of Our Basic Layout

Below are some pictures of the basic layout of our standard hot tub equipment package as well as the required dimensions needed. These are only a few of the many possible layouts and depending on your own situation and imagination your final results may differ.

Remember when designing and installing your equipment layout that occasional maintenance is required and the more accessible things are, the easier it will be.

Please Note – The 100K BTU heater stands 25½” tall and it requires a minimum of 36″ of clearance above it to a combustible surface regardless of whether it’s installed indoors or outdoors. The actual dimensions of the 100K BTU heater are 15½” x 14¼” x 25½” tall. The optional 150k BTU heater measures 21½” x 18″ x 31¾” tall and also requires a minimum of 36″ of clearance above it to a combustible surface.

The filter stands 30″ tall and requires an additional 20″ clearance above for maintenance access (a total of 50″).


The TOTAL FOOTPRINT of this layout is 58″ x 29″ with the PAD SIZE of 54″ x 18″. The gas line enters the heater on the lower left side, and the electrical line on the right.


The TOTAL FOOTPRINT of this layout is 32″ x 39″ with the PAD SIZE of 32″ x 24″. The hole in the lower right of the heater is where the gas line enters.

Accepting Delivery of Your Hot Tub

Accepting Delivery of Your Hot Tub – BIG BOXES ON A BIG TRUCK


The majority of our hot tubs and complete hot tub systems are delivered by Yellow Transportation (deliveries within the state of California are done through DHL).

On the day we ship your tub to you we will call you to let you know that it’s shipping and to tell you the number of packages and the “pro number” (tracking number).

Once the shipping company has your shipment at its docking facility closest to you they will call you to arrange delivery.   Keep in mind that the size of your shipment is rather large. Complete gas fired hot tub systems consist of three ‘packages’, the hot tub bands (approx. 60#), the heater (approx. 115#) and everything else in a VERY big box (roughly 3′ x 3′ x 6′ weighing about 500#).

forklift-smallElectrically heated systems consist of only 2 packages, the bands and the big box as shown in the picture to the right.
When arranging delivery with the shipping company there are a couple of thing that may need to be considered for an easy delivery. First, let them know if there may be a problem in navigating a large truck to your home.

Trucks smaller than the standard ‘tractor trailer’ are available. The second, and more important consideration is how to get a 500 out of a trailer 5′ off the ground. Unless you happen to have a forklift sitting around, you may want to request a truck with a lift gate.

Please note though, there is frequently an additional charge by the freight company for a lift gate. Many people simple unpack the box right from the truck (usually this only takes 5 to 10 minutes).

liftgate-1With a lift gate you can generally expect some assistance from the driver in getting your shipment from the truck to the sidewalk. If it’s a straight smooth surface into your garage or area where you’ll store the tub till ready to install you may be able to use the drivers pallet jack.

Our hot tubs are packaged with the utmost of care. Consultation with various shipping companies over the years has resulted in a method of packaging that can withstand thousands of miles of bouncing down the road, crashing into by forklifts, and even hours of sitting out in the rain.

Once your shipment is off the truck however, inspect the package carefully for any exterior damage. If any damage is seen make note of it on your “bill of lading”, or better yet open the package and inspect the contents. Also check the bill of lading as to how many packages are in your shipment and MAKE SURE this is the number you receive.