How to Prop Up a Porch Roof

Form a 3-by-10-inch beam using two 2-by-10s nailed together. Your beam must be a little longer than your porch roof is wide.

Tear out a section of floorboard at each end of the porch, 2 feet wide. Set cinder block or other pavers on the ground below the porch inside each hole as a footing for your temporary support beams.

Measure from the bottom of the porch roof to the top of your paver footing in each location. Subtract 9 1/4 inches for the height of the support beam and cut a 4-by-4 post, to that height, for each end of the porch.

Create a jack post, using a third 4-by-4. Set a 12-by-12 scrap of plywood on the front edge of the porch underneath the front beam to reinforce the porch boards where the jack will be set. Set a bottle jack or screw jack on top of the plywood. Measure from the top of the jack to the bottom of the beam and cut the 4-by-4 to fit. Set the 4-by-4 jack post on top of the jack and jack the post up until it is holding most of the weight of the porch. Give the jack two more pumps or one full turn past that point.

Hold the 3-by-10 beam in place under the porch roof. Make sure the ends run underneath the outside beams of the porch at either end and are positioned directly over your paver footings.

Set one 4-by-4 temporary support in place underneath the beam. Knock it into place with a 3-lb. hammer if needed. Use a level to make sure the 4-by-4 is plumb. Set the second 4-by-4 in place underneath the beam and knock it tight with the 3-lb. hammer. Use the jack to lift slightly if the post has too much trouble standing upright. Use the level to check it for plumb.

Toenail the top of both 4-by-4s to the 3-by-10 beam.

Remove the existing porch support pillars, if required, using the jack for additional lifting. Make whatever repairs or replacements are needed and replace your pillars as soon as possible to avoid unwanted sagging.