UUBG-007+4     2007-09-06     [ Catalog ] [ Topics ] [ Index ]
Project: Replace Fiberglas Roof in Office

Contents

  1. Overview
    1. Project Phases
    2. Subsidiary Documents
  2. Assess Needs
  3. Plan
    1. Flat Roof Too Dreary
    2. Clerestory Windows
    3. Insulate Walls
  4. Design
    1. Plan and Elevation Drawings
    2. Construction Strategy
    3. Details
  5. Resources
    1. Work Crews

Scope

Project to replace the fiberglas roof and walls of the administrative office building. Modify the chimney - style skylight for better energy efficiency. Discuss: need, plan, design, time, money and progress.

Summary

REV+4: Construction complete.
TODO: Experiment with fan on timer. Solve chimney - skylight. Seal against vermin and winter weather.


Overview

Project Phases
Phase Completed Remaining
Assess Chat w/ Ben Platnik, Greg Brown.
Survey roof and take interior measurements.
Verify foam roof slopes toward the south.
Plan Clerestory wall and pitched roof approved.
Design Scale drawings and bill of materials.
Workflow, personnel and crews assigned.
Execute Preparation, Demolition, Construction, Drywall & Painting. Remove staples, paint windowsills.
Followup Test fan, hide wiring, cover in winter.
Solve the chimney - skylight problems.
Seal against vermin on north and west walls.
Seal around wall mounted air conditioner.
Subsidiary Documents

This is a large project. Subsidiary documents (UUBG-007-NN) cover design and work details.

Design Drawings

These are drawings in SVG format. Don't worry - your browser probably won't be able to display them. Why? because commercial software can't exploit an open standard -- but I digress...

Work Crews

The work is divided into sub-projects. Each has a crew with its own leader, responsibilities and documentation.

Assess Needs

There is a constellation of energy efficiency problems with the administrative office building. It was originally designed as a Sunday school classroom to engage children with the natural world and our delightful mediterranean climate. To that end it has a garden wall built into the hillside with fiberglass ceiling and walls and screen door flaps which open for ventilation. A custom chimney-style skylight operates as a passive ventilation system. The roof was, for the time, a cutting-edge foam insulation design.

Sadly, the building has been put to quite different uses since then. As a full-time administrative office space, the residents expect heat in the winter and air-conditioning in the summer. The building's open-ness to the environment makes these expectations very expensive. Worse, we are using electricity for both heating and cooling.

Long term, the building is simply unsuitable to the purpose. Plans are being discussed to build a new administration building or completely remodel another one. In the near term, summer is coming and air-conditioning is more expensive every year.

There are three prominent features that undermine insulation and energy efficiency:

  1. 170 sq ft section of the roof is ribbed fiberglass
  2. 100 sq ft of wall is sheet fiberglass
  3. 20 sq ft chimney-style skylight / ventilator
Plan
Flat Roof Too Dreary

The brute force approach would be to replace the fiberglass section of the roof with a flat insulated roof over the existing 2x8 rafters, putting fiberglass between the rafters and sheet rock ceiling. Mineral surface roll roofing would be cheaper and simpler than trying to continue the exotic foam roof over this section. Similarly fill the walls with fiberglass insulation between the studs, covering the exterior with T1-11 plywood to match the rest of the building and sheet rock on the inside. Finally block off the ventilation skylight inside or cover it on the outside. The result would be most forbidding - a low-ceilinged, possibly dank corner, bereft of light or ventilation.

Clerestory Windows

A more enlightened approach is proposed. Instead of filling in the ceiling between the existing 2x 8 rafters, pop a pitched roof up on a new set of rafters which ride above the existing rafters. These are supported by a short wall with a couple of clerestory windows looking southward. The ceiling is designed to reflect light down through the existing rafters. Include a small ventilator fan on a timer to cool the building off in the evening and pre-dawn hours of summer. Windows openable with screens?

Insulate Walls

With light and ventilation provided through the ceiling, it should be fine to fill in the walls with standard construction. Remove the translucent fiberglass panels. Replace with T1-11 panels outside, R-12 insulation, sheet rock inside.

Defer dealing with the chimney-style skylight until after the roof is replaced. Then try simple things first - blocking off gross airflow. See how it goes.

Design
Plan and Elevation Drawings

UUBG-007-02 Office Roof Plan & Elevation is a composite view of the design. The upper portion is a plan view showing the existing rafter layout of the north wing of the office. These rafters are presently covered by ribbed fiberglass. The lower portiion of the drawing is the east elevation of the new roof featuring a short wall with clerestory windows.

The rightmost (north) wall of the office is buried in the hillside with the odd angles illustrated. Pitch the new roof (F) to meet the top of the original rafter layer (A) in the far right (northwest) corner. The nearer rafters (A) are shorter than the westmost one, so the new roof won't quite meet any of the rest of them. New facia board covering the north ends of the rafters will have to be cut to fit the triangular and trapezoidal spaces. At the east wall, there is a full 8" gap between the bottom of the new rafter and the old. Use four plywood sandwidches (C) over 2x4 risers to secure the new rafters (D) to the shortest old rafters (A). Run a 13" high shear panel (E) across the fronts of the sandwich panels (C) to the far wall. The rafters without sandwiches will have 2x4 x 22" risers to carry the shear wall all the way across.

The clerestory wall (B) has a couple of windows for light and ventilation. The new roof (F) has a white sheet rock ceiling underneath to reflect light into the space below through open rafters (A). The sheet rock continues down the face of the shear wall (E) and across the bottom of existing rafters northward. Add cleats below the shear wall to attach sheet rock as it passes down between the existing rafters.

Construction Strategy

Frame the clerestory wall (B) on the ground then hand it up. Fasten wall (B) in place across rafters (A). Tack on a couple of buttresses to hold it vertical. Pre-assemble the four sandwich panels (C) with 7" and 12" risers inside then hand them up. Screw panels (C) in place on first four rafters (A).

Cut longest (westernmost) 2x6 rafter (D) to length (~16 feet?). Trim top end at 76 degree angle so face is vertical when installed. Cut 3.5" wide 14 degree right angle notch about 18" from top end to mate with wall (B). Trim bottom end at 14 degree (very shallow) angle to lay on existing rafter (A). Hand up this long rafter and lay in place. Screw bottom end onto existing rafter (A) in northwest corner.

Details
Resources
This is a lot of work to be done in a short period of time. The key is to organize the work to be carried out by several small crews. The work is divided into sub-projects.
Work Crews

Each has a crew with its own leader, responsibilities and documents. Follow the links for details.

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