I have about a 1400 square foot roof with a 6/12 pitch. The house was built in the 50's and there are no soffit vents, but there are 2 Gable ends. I need to have a new roof installed and am adding a ridge vent. Is it ok to leave the gable ends with a ridge vent or should I close them off and have edge vents installed? I have no overhang to add soffit vents. Any insight would be very helpful.
With a 1950's house, this would be a good time (since you are re-roofing anyway) to consider adding a "double roof" to address both insulation and ventilation. From the existing roof deck, that would be 4-6" of rigid foam, 2x4's to make a ventilation channel above the foam, and plywood for a new roof deck, followed by the new roof.
There are a lot of factors that involve venting in attics. The size of your attic, the amount of sun your roof gets, climate, the amount of directional wind, and so on.
To best serve your situations (in most cases) would be to install some sort of soffit venting and the ridge vent. Depending one where in relation to the attic floor the gable vents where installed I would either close the top 3/4 of them or everything. Good soffit ventilation with a ridge vent is usually a perfect scenario. When you mix gable vents with ridge vents you can often get airflow OUT the gable vents which means your ridge vents are sucking in the hot air from above. This effect causes a situation where you have a pool of hot air and humidity circulating amongst the dead space at the top of your attic, in between the height of the gable vent and ridge.
But you don't really have a choice on your gable vents. You have to keep them open or all of the hot air in your house will be sucked up. In this scenario I would try to add more blown in insulation so that the height of the insulation reached the bottom of my gable venting so that there is an intake deck.
The other option is that your house was built in the 1950s, hasn't had any issues (I am assuming), so don't just add a ridge vent because that is the new thing. Make sure that there is a reward (how hot is your attic) for the risk.