Appendix D:

Constructing a Seedhouse

Seedhouse Features

Building the Seedhouse Frame

Seedhouse Tables

Seedhouse Ventilators

Covering the Frame

Finishing the Seedhouse

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Seedhouse Features

Growing plants from seed ahead of the normal planting season has a number of advantages, including stronger and more vigorous plants, earlier maturation, larger yields, and reduced costs on weed and insect control.

There are many types, sizes, and shapes of greenhouses, but not every design or shape or structure is best suited to grow quality seedlings.

This appendix provides instructions for constructing a seedhouse which is simple in design, easy and quick to construct, inexpensive, and highly functional. This seedhouse design simplifies growing procedures, produces strong, healthy seedlings, and minimizes effort and care.

Features of this seedhouse include:

A seedhouse frame made with 4 x 4 posts and 4 x 4 stringers.

Plastic covering.

Three rows of tables inside the greenhouse for growing seedlings.

The same types of tables outside the seedhouse for hardening plants off before transplanting.

Ventilators along the length and south side of the seedhouse for adequate circulation.

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Building the Seedhouse Frame

Step 1: Select a Building Site

Select a level area large enough to accommodate the seedhouse with additional space for expansion, should the need arise.

Avoid shadows from trees and buildings. Full sunlight is essential to produce healthy plants.

In the Northern Hemisphere, face the length of the structure east and west. This gives the broadside a southern exposure and captivates more of the sun’s heat during the winter season.

Step 2: Purchase Materials

Purchase your materials. The size of the seedhouse depends on your needs. We will illustrate with a seedhouse 20’ wide, 40’ long, and 8 ½ feet high at the peak.

The table on the following page shows the materials you will need to build either a 20’x 40’ or 15’ x 30’ seedhouse.

Tip If you plan to paint your seedhouse, it will be easier, faster, and you won’t get paint on the clear plastic cover if you paint it now!

© 2003 Food For Everyone Foundation
Seedhouse Materials List

Seedhouse Size

Material Description	20’ x 40’	15’ x 30’
4” x 4” - 8’ Side Posts (cedar preferred)	20	8
4” x 4” - 10’ Center Posts (cedar preferred)	5	4
4” x 4” - 20’ Stringer	8	6
2” x 3” - 10’ Rafters & End Studs	60	46-8’, 4-10’
2” x 3” - 6’ Wall Studs & Doors	40	30
2” x 3” - 3’ Table Legs (incl. Outside Tables)	200	180
2” x 4” -16’ Table Base	25	20
1” x 8” -10’ Skirting	12	9
1” x 4” - 10’ So. Side Vent. Base	4	3
1” x 4” - 6’ Table Tops	320	300
1” x 4” - 4’ Cross Braces	17	12
1” x 2” - 10’ Ventilators	16	12
4” D Hinges	4	4
20’ x 42’ Plastic Side Covering (6 mil or better)	2	2( 15’ x 32’)
20’ x 42’ Plastic End Covering	1	1 (15’ x 32’)
3” Box Nails	15#	12#
5” Box Nails	15#	12#
1 ¼ “ Lathe Nails	10#	8#
Black Roofing Paper (3’)	120’	90’
1 ¾” x 48” Lathe	325	200
White Exterior Paint	3 gallons	2 ½ gallons

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Step 3: Measure and Stake the Structure

After clearing and leveling the site, measure and stake the size of the structure.

Step 4: Mark Spots for Posts

Mark the spots for the 4 x 4 posts used to frame the building. The space between the posts is 10’ each way.

Step 5: Dig Post Holes and Install Posts

Dig the holes and install the 4 x 4 side posts along the sides of the seedhouse. Set the 8’ long posts in the holes 18” below the level of the floor (soil) surface. The top of the posts on the sides of the structure are 6 ½ feet above the floor level.

Side Posts

Step 6: Nail Stringers on Top of Posts

After the side-posts are secure, nail 4 x 4 stringers 20 feet long on top of the posts.

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Step 7: Prepare Center Posts

Prepare the center posts. Before the center posts are lowered in the holes, they need to be notched. Measure 18” from one end of the posts on one side of the 4 x 4’s and cut a notch 1 ¼ inch deep x 3 ¾ inches wide above the 18” mark. Do this on one side only of all center 4 x 4 posts.

Center post with notch

Step 8: Place Center Row of Posts

Place the row of posts in the center of the structure. When the posts are set in place, the notches should face south. The posts are 10’ long set 18” deep in the ground. They are 8 ½ feet high above the floor level.

Step 9: Nail Stringers to Tops of Center Posts

After the posts are secure, nail one row of 4 x 4 stringers 20’ long on top of the posts.

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Step 10: Nail Second Row of Stringers

Nail a second row of stringers 18 inches below the first row of stringers. Before nailing the second row of stringers to the posts, notch one side of the stringers to match the notches made on the posts. Match the notches to fit into each other and nail securely.

Center posts and stringer assembly.

Step 11: Make the Roof

Make the roof of the building of 2 x 3 wood rafters 10’ long. The space between the rafters is 24”.

Make the roof support for the north slope. Cut the rafters for the north slope to fit and toe-nail one end into the 4 x 4 stringer at the peak, flush with the top edge. Nail the lower end on top of the 4 x 4 stringer flush with the outside edge.

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Roof assemby.

Step 12: Nail Side Studs to Frame

The studs along the sides of the frame are 2 x 3’s that are 6’ long. Space them 24” apart to match the roof rafters.

Nail the top end of the stud to the underside of the 4 x 4 stringer and flush with the outside edge. Nail the lower end of the studs to a 1 x 12 board 20’ long nailed near the floor level to the 4 x 4 posts on the outside of the frame.

Step 13: Make Roof Support for South Slope

Make the roof support for the south slope by nailing both ends of the 2 x 3 rafters on top of the 4 x 4 stringers. Nail the rafters for the south-sloped roof to the second (lower) row of 4 x 4 stringers. Nail the ends flush with the outside edges of both stringers.

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Step 14: Frame the Ends of the Building

Frame the ends of the building with 2 x 3 studs. Cut to fit and nail the studs in place. The space between the studs is 24 inches, except for the doors.

Studs are 24 inches apart on center.

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Step 15: Install Doors

Doors should be 30” wide x 6’ high. Construct the outer frame from 2 x 4’s. Then notch 1 x 4 diagonal braces into the back of the door.

Cold winds blow from the northwest or north. Therefore, the door hinges should be installed on the north side of the door frame. When the doors are opened, they will tend to block the wind from blowing on the plants in the greenhouse.

Door assembly.

You have now completed the frame of the seedhouse.

© 2003 Food For Everyone Foundation

Seedhouse Tables

Constructing a seedhouse without tables would be a mistake. Seedlings should never be placed on the ground, even when growing in full sun.

Here is how the tables should be configured when completed:

The tables are 30” high

There are two side tables 36” wide

There is one center table 72” wide

The aisles between tables are 44” wide

Follow these steps to construct the tables:

Step 1: Stretch a Chalk Line for Tables

Measure 30” from the inside edge of the 4 x 4 side posts. Stretch a chalk line tight the length of the seedhouse.

Step 2: Drive Studs into Ground for Table Legs

Point one end of the 2 x 3 studs which are 36” long. Drive the studs 10” into the ground in line with the chalk line. Drive a stake every 28 inches.

Step 3: Level the Table Leg Studs

Check the top of the table legs. They must be level. Each table along the sides of the seedhouse has two rows of table legs. The center table has three rows of table legs.

Step 4: Nail 2 x 4’s to Table Legs

With the table legs in place and level, nail 2 x 4’s standing on edge to the top of the table legs.

Step 5: Nail Top Boards on Side Tables

Nail 1 x 4’s that are 36” long across the two rows of 2 x 4’s. Put a space of 1” between the 1 x 4 boards.

Step 6: Construct Center Table Legs

Construct the center table the same way, except use only one row of table legs along the center row of 4 x 4 posts.

Step 7: Nail on Center Table Tops

Nail 1 x 4 boards 72” long across the three rows of table legs. Put a space of 1” between the boards. There will be a 6” overhang along each side of the table.

Center table assembly.

You have now completed building seedhouse tables

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Seedhouse Ventilators

Uniform, adequate, and even ventilation throughout the seedhouse is essential to uniform growth of seedlings.

The ventilators are located at two openings along the full length of the seedhouse: one just below the peak and another along the south side of the seedhouse.

The 18” opening along the length and ridge of the building, just above the south-slope roof is a continuous ventilator. This simple ventilator eliminates fans and cooling pads, yet effectively controls the temperature throughout the seedhouse.

To Make the Ventilator at the Peak

Step 1: Get Sheet of Plastic

Take a sheet of clear 6 mil plastic 24” wide x 40’ long.

Step 2: Nail 1 x 2’s to Plastic

Lay 1 x 2’s of random length in a straight line on and along the length of the center table. Place one edge of the plastic sheet on the 1 x 2’s. Place another row of 1 x 2’s on top of the plastic and on top of the first row of 1 x 2’s. Nail the two 1 x 2’s together securely with the plastic between.

Step 3: Attach Other Edge of Plastic to Stringers

Take the other edge of the plastic and, using lath, nail the plastic to the 4 x 4 stringers at the peak. The ventilator is in place.

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To Open and Close the Ventilator

Step 1: Fasten Metal Pulleys on North-Slope Rafters

Fasten a metal pulley on each north-slope rafter in line with each center 4 x 4 post. Fasten the pulley 24” down from the peak.

Step 2: Fasten Hooks on Center Posts

Approximately 14” above the table top fasten a hook or nail on each center 4 x 4 post.

Step 3: Attach Clothesline Rope

Take a length of clothesline rope and fasten one end securely to the 1 x 2 strip holding the plastic sheet (ventilator). Thread the rope through the pulley on the rafter and bring the end down to the hook on the post. Give the rope 18” extra length and cut it off.

Step 4: Tie Loops in Rope

Tie three loops on the rope; one on the end and the other two 12” apart from the end.

Use the ropes to regulate the amount of ventilation desired in the seedhouse.

To provide full ventilation, pull the ventilator to the full opening and anchor the ropes to the hooks on the posts.

To close the ventilator, simply unhook the ropes. The ventilator closes automatically. Because it is on the inside of the seedhouse, it is not affected by the wind.

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To Make the Side Ventilator

Follow these steps to build the 18” ventilator along the south side of the seedhouse.

Step 1: Attach 1 x 8 Boards

Before you pull the cover over the seedhouse frame, nail 1 x 8 boards 20’ long in a straight line 18” below the top of the studs.

Step 2: Tack 1 x 2 Boards in Place

On the top edge of the 1 x 8’s place 1 x 2’s running the full length. Tack the 1 x 2’s only enough to stay in place.

This ventilator is not yet completed until after the seedhouse cover is installed.

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Covering the Frame

Only two operations remain to complete the seedhouse. You will need cross bracing to strengthen the frame structure, and you will need to cover the frames with clear plastic film.

For added strength and stability, use 1 x 4’s that are 48” to 60” long for cross-bracing in the building. Nail these to the posts, rafters, and stringers.

Special formulated transparent plastic at least 6 mil thickness is sold in rolls of varying widths and lengths. The best materials have a life span of 6 to 9 years. To cover the sides and roof of a 20’ x 40’ seedhouse will require two sheets 18’ wide x 40’ long. To cover the ends of the seedhouse will take two sheets 9’ wide and 20’ long.

Covering a structure with plastic film is fast and easy—providing some precautions are used.

IMPORTANT:

Cover the north side and north roof with one sheet first. Attempt this only during the part of the day when the air is very still.

Step 1: Pull the Plastic Sheet over the Frame

Pull the sheet over the frame. Have the lath ready and very quickly lath the plastic to the rafters.

Step 2: Nail Plastic Sheet in Place

Use 1 ¼” lath nails and nail a lath to every 3rd or 4th rafter and upright stud as quickly as possible. This is a precautionary measure to hold the plastic in place in case of wind.

Step 3: Secure Plastic on Every Rafter

Nail lath on every rafter and stud. The plastic must be secured with lath on every rafter and stud.

Nails on the lath should be 8 to 12 inches apart. When nailed to the rafters, the lath should be tight to hold the plastic secure against flexing between the lath and the rafter or stud. When

lathed to the rafters and studs as recommended, the plastic will not flex or tear and will weather strong winds for many years.

Step 4: Secure Plastic to South Side

After securing the plastic on the north side, pull a sheet of plastic over the south roof and side.

Follow the same procedure in fastening it securely as outlined for the north side.

Step 5: Secure Plastic to Ends of Structure

After completing the south side, take a sheet of plastic 9’ wide x 20’ long and cover each end of the building. Nail lath to every upright stud. Before covering the end, hang the doors in place. The plastic covers the end including the doors.

Use lath to secure the plastic to the doors. After lathing the end and doors, cut the plastic along the door frames. The doors are free to move open and shut on their hinges.

Inspect to be sure the plastic is securely lathed to every rafter and stud.

You have now completed the seedhouse frame with plastic.

To Complete the South-Side Ventilator

Step 1: Nail 1 x 2 Strip and Cut Plastic

Previously, you placed a 1 x 2 strip of lumber on the top edge of the 1 x 8 board along the south side of the structure. The plastic covers the 1 x 8 board and the 1 x 2 strip.

Take 1 x 2’s and nail a strip over the 1 x 2 strip under the plastic. Nail the 1 x 2’s securely together. Next, cut the plastic along the line separating the 1 x 2 from the 1 x 8 board. This separates the plastic and frees the 1 x 2.

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Step 2: Roll Up Plastic to Open Ventilator

To open the ventilator, turn the 1 x 2 strip and roll the plastic up. When rolled up, you can hold the ventilator open using short lengths of clothesline rope attached to the rafters and hooked.

Step 3: Unhook Ropes to Close Ventilator

To close the ventilator, unhook the ropes and let the plastic unroll.

Finishing the Seedhouse

To strengthen, stabilize, and secure the seedhouse, use pieces of lumber such as 1 x 4’s that are 48” to 60” long for cross braces. Nail cross braces to the posts, rafters, and stringers.

We recommend painting your seedhouse. Painting gives a finished appearance, preserves the wood, and increases the light factor in the greenhouse.

Build outside tables with flat, level tops 30” high so they are in full sun close to the seedhouse. Use the same construction procedures as you used to build the tables in the seedhouse. These tables are necessary for “hardening off” the seedlings before they are transplanted into the field or garden.

Plastic-covered greenhouses require some type of shading to lower the temperature and diffuse the bright sunlight during hot weather. Otherwise, the leaves on young seedlings will scorch from sunburn and the plants will die.

There are several types of synthetic materials available to use as shading. You can purchase these to fit nearly any size structure, and in various shading percentages. When temperatures are above 95 degrees Fahrenheit, you need 62 to 68 percent shade density.

This type of shading is quick and easy to use. Just pull the shade-cloth, called milar, over the greenhouse frame—plastic cover and all—in one sheet. The shade cloth provides uniform shade throughout the seedhouse and effectively lowers the temperature inside of the seedhouse.

During hot weather, you can stabilize the temperature in the greenhouse by opening the doors and the continuous ventilator and covering the greenhouse with shade cloth.

During short days and cooler weather, plants do best in full light. To accomplish this, just pull off the shade-cloth and store it properly until needed again.

© 2003 Food For Everyone Foundation