Figure 1

Drawings and Specifications
for a Greenhouse/Addition

by Stuart Culp
Click figures to enlarge


A. General

This document contains the drawings and specifications for the construction of a residential greenhouse attached to the dwelling at (Location). Figure 1 shows an artist's sketch of the existing dwelling, the polar orientation and the location of the addition. Figure 2 shows the east elevation and Figure 3 shows the north elevation. The 14' x 20' x 8' greenhouse shall maintain a semi-tropical environment during the entire year for the purpose of housing a private horticulture collection. Integral to the greenhouse is an enclosed passageway which shall allow comfortable access to the greenhouse from the dwelling under all weather conditions.

The construction of the greenhouse and passageway shall be aesthetically similar to the main dwelling. The greenhouse meets the Town of (your town) side and rear offset requirements of 10 feet and 30 feet, respectively. The actual offsets are approximately 62 feet from the rear and 25 feet from the side. 

Figure 2

Figure 3

B. Construction

Construction of the project shall be divided into two phases. Phase I includes site layout, excavation, grading, foundation, passageway, and utilities. Phase II includes the greenhouse framing, glazing and equipment.

Phase I

a. Site Layout -- The addition shall be square with the main dwelling.

b. Excavation -- Excavation includes that necessary for the foundation and utilities.

c. Grading -- Grading includes that necessary for foundation backfill and the lawn area designated on Figure 4 to prevent water runoff from accumulating against the foundation. Some grading is also necessary inside the greenhouse. Note that there is about one foot of slope from greenhouse end to end. It is desired to level the interior finished soil surface and the door sills with the lowest point of the outside soil (the north end). The interior finished soil shall be one foot in depth, achieved by removing the existing clay/shale hardpan and replacing it with topsoil.

d. Foundation -- The foundation shall be constructed so that footings are below the frost line in accordance with Figure 5. Note that the two doorways to the greenhouse are to be at approximately ground level for ease of entrance, requiring that the foundation be relieved at those points. Foundation insulation is to be applied to the passageway as well as to the greenhouse. Dimensions relating to the passageway and the distance of the greenhouse from the main dwelling are nominal. Dimensions relating to the greenhouse proper are measured along the outer surfaces of the framing and are exact. The greenhouse length dimension is arrived at in the following manner (see Figure 9 and Appendix A1, A2, and A3.): Sheet width = 4'. H profile = 5/8". Assembly tolerance and thermal expansion (each edge) = 1/8". 48 + 1/8 + 1/8 + 5/8 = 48 7/8". This places studs on 48 7/8 / 2 = 24 7/16" O.C.

e. Passageway -- The passageway shall be constructed in a manner similar to the main dwelling. Siding and roof slope shall match except as stated below. The slope of the shed roof above the entrance area to the main dwelling should come as close as possible to the slope of the main roof, however it will probably be limited by the clearance between the roof joist and the door. Compromises in this area may have to be made to achieve a satisfactory appearance. The interior of the passageway shall be left unfinished, and the floor shall be dirt. A pressure-treated wood landing with stairs to facilitate exit from the main dwelling shall be provided. No insulation other than the foundation shall be provided, however the treatment of the wall under the siding shall be consistent with typical, well insulated house construction. The entrance doorway to the passage shall be located as close to the family room window as practical. This will be the limiting factor as to the start of the passageway. The door shall be a standard 2' 6" door similar to other interior doors used in the downstairs area of the house. A portion of the family room baseboard heater will have to be shortened to make room for the door, and electrical wiring in the wall may have to be relocated. The clothesline canister shall be relocated to the north wall of the passageway. The floodlight shall be relocated, but the relocated position is yet to be determined. It is desired that there be no wood exposed to the weather (no painting).

f. Utilities -- Hot and cold water, natural gas and electricity are to be supplied to the greenhouse electrical box, heater and sink as shown in Figure 4. Gas and water connections shall be provided with shutoff valves at both ends of the lines. Water valves at the house end shall be equipped with drains. The hot water pipe shall be insulated. Water pipes shall be underground to provide freeze protection.

Phase II

a. Greenhouse Framing--All lumber exposed to the greenhouse interior shall be pressure treated. Nails shall be galvanized and screws shall be stainless steel. Construction details are outlined in Figures 6, 7, 8, 9, 10 and 11.

b. Glazing--The greenhouse glazing material shall be clear, 16 mm triple wall polycarbonate. Glazing, attachment extrusions and related hardware are described in Appendix A1, A2 and A3. Note that it appears as though the extrusions must be slipped onto the panels from the end, because of the difficulty in installing from the side. This being the case, the walls must be installed first due to the roof overhang.

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