Basements, Attics and Crawl Spaces - Attic Ventilation

We recently purchased a home built in 1890 with no attic ventilation.

The home was reshingled for the purchase and the roofer did not add any ventilation. The home is a two story 2500 foot house with a good sized attic. There is a window on each side of the gables in the attic but no room for soffit vents, I think. The eaves are boarded up along the underside of the roofs framing rafters on the outside and not a triangle like more modern homes so I don't think soffit vents are going to work well.

I was thinking of removing both windows and installing square gable vents to replace the windows. They are both centered on each side of the attic and would possibly create a crossflow for air through the attic.

Other than this I would like some ideas of what I can do to add some vents, I am sure it will need vents as the roof was showing signs of ice damming from the previous shingles according to the inspector. He said to just have roofers add vents but the previous owner did not specify this in contract so it falls on us to add something.

I do understand about the formula for vent size to attic space for adding vents like soffit and gable or ridgeline vents.

Any Ideas?

What is needed depends on how modernized the house is. I grew up in a house built in 1917, no insulation anywhere, and the attic sounds a lot like yours. But back then, the houses breathed easily and did not really need attic ventilation. If the attic now has insualtion as well as the walls in the house, then you do need ventilation. The window may be enough, but if insulation is up to modern specs, it will not be. Hip roof or gable?? There are vents made for both, and soffit vents should be added. There are vents available even if there is no overhang eve.

The windows will do more harm than good. The soffit vents need to be in each rafter bay to let air in or you will have ice-dams there. ---From heat escaping from conditioned space through ceiling, rising to heat roof deck = freeze/thaw. Audel Complete Building Construction - Google Books (http://books.google.com/books?id=Z8apR1RkUHUC&pg=RA1-PA608&lpg=RA1-PA608&dq=gable+vent+or+soffit+vent&source=bl&ots=gS6elel5KA&sig=NVC2InoVWlvDkp4eVqT1UA_QZBo&hl=en&ei=8h0KSqSpLKTgtAPf5ezhCA&sa=X&oi=book_result&ct=result&resnum=9#PRA1-PA604,M1) Figure 150 / attic space, not as in article.
Fill all holes in ceiling with fire-stopping foam if lights or pipes, ducts and metal around gas vent. Use continuous soffit and ridge vents with baffles 50/50 for best results. A power vent leads to mold: Ron Hungarter investigates black mold with Air Vent, Inc. (http://www.ronhungarter.com/black_mold.html)
No soffit --- Cor-A-Vent : IN-Vent (http://www.cor-a-vent.com/in-vent.cfm)
Be safe, Gary

Problems with adding anything to roof where shingles are is the shingles are brand new and I really don't want to rip up some to add venting unless its a smaller area. Adding vents along lower portion that require removing a few rows of brand new shingles seems a bit of a waste.

I understand I need venting but wanted solutions that don't really require removing new shingles.

Thanks for the ideas.

Jeff